literature review of sources of water

Literature review: Water quality and public health problems in developing countries

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Eni Muryani; Literature review: Water quality and public health problems in developing countries. AIP Conf. Proc. 23 November 2021; 2363 (1): 050020. https://doi.org/10.1063/5.0061561

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Water’s essential function as drinking water is a significant daily intake. Contamination by microorganisms (bacteria or viruses) on water sources and drinking water supplies is a common cause in developing countries like Indonesia. This paper will discuss the sources of clean water and drinking water and their problems in developing countries; water quality and its relation to public health problems in these countries; and what efforts that can be make to improve water quality. The method used is a literature review from the latest journals. Water quality is influenced by natural processes and human activities around the water source Among developed countries, public health problems caused by low water quality, such as diarrhea, dysentery, cholera, typhus, skin itching, kidney disease, hypertension, heart disease, cancer, and other diseases the nervous system. Good water quality has a role to play in decreasing the number of disease sufferers or health issues due to drinking and the mortality rate. The efforts made to improve water quality and public health are by improving WASH (water, sanitation, and hygiene) facilities and infrastructure and also WASH education.

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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

Scribbr slides are free to use, customize, and distribute for educational purposes.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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• Published: 21 March 2024

PV to reduce evaporative losses in the channels of the São Francisco’s River water transposition project

• Uri Stiubiener 1 ,
• Adriano Gomes de Freitas 1 , 2   na1 ,
• Janne Heilala 3   na1 &
• Igor Fuser 1   na1  

Scientific Reports volume  14 , Article number:  6741 ( 2024 ) Cite this article

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• Energy grids and networks
• Energy infrastructure
• Engineering
• Environmental impact

Open water transposition channels in hot and arid regions, like those in the São Francisco River Integration Project (PISF) in Brazil, suffer significant water losses through evaporation. This paper proposes covering these channels with photovoltaic (PV) panels to reduce evaporation while simultaneously generating clean energy. The research aims to quantify water savings and energy generation potential across all channel lengths and assess whether the generated solar power can substitute grid electricity for powering the transposition pumps during peak hours, thereby enhancing energy efficiency. This study analyzed the state-of-the-art of PV generation and calculated their solar potential. Identified the specific characteristics of PISF channels and watercourses considering the regional geography, meteorology, irradiation, and social peculiarities. And, finally, assessed the feasibility of covering the watercourses with solar panels. The results reveal that covering all current PISF channels with PV panels could save up to 25,000 cubic meters of water per day, significantly contributing to water security and improving the quality of life for the local population. Additionally, the project could generate 1200 gigawatt-hours of electricity annually, meeting the energy demands of the transposition pumps during peak hours and promoting energy efficiency within the project. This research paves the way for utilizing PV technology to address water scarcity challenges and enhance the sustainability of water infrastructure projects in arid regions worldwide.

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Introduction

This research aims to evaluate the potential water savings achieved by covering water courses with photovoltaic solar panels. Additionally, it will assess the improvement in energy efficiency of the São Francisco River Integration Project (PISF) by utilizing solar energy to power its pumping system during daylight hours.

The PISF addresses a historical demand for water resources in Northeastern Brazil. This region houses 28% of the population with access to only 3% of the country’s total water resources. The São Francisco River supplies 70% of the region’s water, historically impacted by severe droughts. Projected climate change and global warming scenarios suggest prolonged and intensified drought periods, highlighting the critical importance of water security for the region.

The problem

PISF transfers water from the São Francisco River to surrounding arid areas. However, solar radiation directly heats the water and adjacent concrete walls, of the trapezoidal shape channels leading to increased evaporation through a “hot zone” effect over the channel (Fig. 1 ) due to mirror effect.

Hot zone due to the sun radiation on channel’s concrete borders.

Water loss is calculated based on the open water surface area and local evaporation rates. Circa 30% of the captured water is lost through evaporation. PISF’s components are subjected to the same climate conditions and environmental variables. The volume of water lost by evaporation EVP was obtained from Eq. ( 1 ) where \(A_{(i)}\) is the free water surface and the local evaporation rate obtained from the National Institute of Meteorology (INMET) measuring stations is \(evp = 3,150~{mm/year}\) .

At the North Axis, 16.4  \(m^3/s\) of water is captured from the river. Approximately 5.4  \(m^3/s\) is lost through evaporation (90% of these in the reservoirs), leaving only about 11  \(m^3/s\) with a useful destination (distribution to supply the population) 1 . At the East Axis, 10  \(m^3/s\) of water is captured and only about 7  \(m^3/s\) supplies the population.

De Farias, Curi, and Diniz calculated water losses using the AcquaNet simulation model in several scenarios and analyzed the performance of PISF’s East Axis serving the Paraíba River Basin. They found total loss ranging from 48 to 60%. Of this, 3.5% to 6.9% were attributed to evaporation. Leakage and in-transit losses respond to complete the total loss 2 .

As water is the subject of this project, initiatives to reduce losses due to evaporation must be considered

Proposed solution.

By covering water courses with photovoltaic solar panels, this research seeks to achieve two key objectives:

Reduce water evaporation: The panels will provide shade, significantly reducing water loss through evaporation.

Generate clean energy: The installed solar panels will generate electricity, potentially powering the PISF pumping system during the day, reducing reliance on grid-based power, and contributing to energy efficiency.

Significance

This research can contribute to addressing the water scarcity challenges in Northeastern Brazil by demonstrating the potential of water-saving technologies and promoting sustainable energy solutions for water infrastructure systems. The findings can inform policy decisions and guide the implementation of similar projects in other regions facing water scarcity and renewable energy integration opportunities.

High water loss from critical infrastructure highlights the importance of addressing evaporation through innovative solutions like covers to improve sustainability. Further research on mitigation strategies is crucial for responsible water resource management. To achieve effective mitigation strategies, the research follows a three-step process:

Literature review: A comprehensive review of academic and industry literature is conducted to establish the current and future outlook for photovoltaic solar energy generation in Brazil and globally.

Characterization of PISF: The structure and characteristics of the channels and watercourses within the PISF are identified and documented.

Geographic and meteorological characterization: The geographical and meteorological conditions of the region are analyzed to better understand the potential impact on the proposed solution.

Evaluation of PV arrays coverage

The research then explores the potential of using photovoltaic arrays to cover watercourses and assess its feasibility for PISF. This involves three key steps:

Coverage area and energy generation: The coverage areas for the photovoltaic arrays \(({S_ {PV}})\) are determined. The surface to be covered by PV arrays \(({S_{PV}})\) , is obtained from Eq. ( 2 ) where \(P_{PV}\) is the peak power of the PV installation, \(\mu _{PV}\) is the power density. This surface was called “Solar Area”.

Energy generation: The expected annual energy generation for PV installations \(({E_{PV}})\) is obtained from Eq. ( 3 ), where  \({\overline{H}}\) is the annual average of, locally measured, daily solar radiation (in  \(kWh/m^{2}.day\) ), \(\eta _{PV}\) is the rated efficiency of the PV panels and PR is the performance ratio of the PV power system.

In this paper, was assumed that \(\mu _{PV} = 1\,MW/10,000\,m^2\) , \(\eta _{PV} = 15\%\) , and \(PR = 0.8\) .

Water savings: The annual water savings \(({Q_ {PV}})\) associated with the coverage area \(({S_ {PV}})\) are estimated based on relevant references 3 , 4 .

Through this comprehensive approach, the research seeks to evaluate the effectiveness and feasibility of employing photovoltaic arrays to reduce water loss and enhance sustainability within the PISF.

Literature review

Water scarcity.

According to the United Nations Development Programme (UNDP), the Human Climate Horizons (HCH) report states: “[...] the weather conditions we experience are changing, resulting in higher year-round temperatures, more extremely hot days resulting in higher year-round temperatures, more extremely hot days [...]” 5 .

This predicts that severe drought and lack of water resources will persist in the region. Warming influences human development and all spheres of our lives, including our health, livelihoods, and ability to work. Water availability is of crucial importance for the local population.

Impacts related to PV installations on water

PV installation on water requires further description and analysis, when the artificial channels were designed and built, the environmental risks were considered 6 . If only channels are covered the impacts on aquatic flora and animal life will be less. However, to shoreline installations, other PISF-free water surfaces, natural rivers, and reservoirs will be covered by floating PV installations, as shown in Fig. 8 . In that case, a new study of environmental impacts and risks should be carried out and approved by the respective legal entities and authorities, extending their installation, changing climate, and synergizing with wave power potential and stakeholders.

Alongside the technical and economic aspects, the socio-environmental aspects must be considered when designing PV installations 81 . Some of these aspects are related to visual impacts, facility safety, impacts on tourism and leisure, impacts on water quality, impacts on aquatic flora and animal life, impacts on bird habitats, etc. Some of these impacts are 7 :

Visual impacts

The large areas occupied by PV installations will bring aesthetic and visual impact. They are subjective and personal. Some people like it, others don’t. Studies indicate that reservoirs covering up to 50% of the wetland area by PV arrays are acceptable in other parts of the world 8 .

High voltage DC power cables, with tension levels of 1.5  kV , used in utility-scale PV plants are relatively near the floor level. The security issue has two aspects: the safety of people and animals in the vicinity of the plant and the safety of installations regarding the physical impacts or short-circuiting effects due to foreign bodies. Currently, there are no technical standards that address these issues. However, it is necessary to establish a region of restricted circulation around the PV array. Equal importance should be given to the training of a skilled technical workforce to work with PV facilities.

Jobs, tourism, and leisure

These impacts result from the two previous items: the social perception of the beauty of the installation and the security perimeter. Transposition channels are not leisure areas. Rivers, lakes, and reservoirs should be studied in accordance with the multiple uses of these water bodies and the appropriate regulations.

Clean water flow in PISF channels can host fishing farms, introducing farmed aquaculture as a new activity in the region reducing poverty and increasing the local employment and food security 3 . PV will bring new job vacancies to the neighborhood. The operation and maintenance of PV facilities require technically educated people for the necessary operations. Other job openings, as well as indirect jobs and services needed to serve new employees, and their families, will emerge.

Water quality

Some water quality parameters may be more affected by covering channels, whereas others are slightly affected. Water pH, total dissolved solids, electric conductivity, and alkalinity are less affected. Dissolved oxygen (DO) and algae concentration, seem to be significantly affected by channel coverage. As a result, the nutrients and phosphorus are impacted, as they are related to algae concentration in water.

El Baradei and Al Sadeq investigated the water quality in channels covered by PV arrays. They found that the channel coverage will not harm algae, nutrients, phosphorus, pH, and alkalinity. They found that the ideal rate of covering the Sheikh Zayed Canal, in Egypt, to optimize the power production, water quality, and water loss through evaporation, is between 33 and 50% 9 . They suggest that a water quality simulation should be done, for every “solar canal” of fresh or irrigation water project, in order to meet the water quality standards.

Floating PV arrays are relatively recent facilities, all less than 10 years old. No negative impact on water quality has been reported in these facilities to date 10 . According to Rosa-Clot and Tina 8 , materials in contact with water are not polluting. Reports demonstrate that shading does not affect, or even benefit, the water quality 10 , 11 .

The transposition channels have no vegetation and the water must not be contaminated with organic matter. PV arrays on natural water surfaces shade but do not block the incidence of light on the water surface. Shading of the aquatic surface may have effects on vegetation and micro-algae in the reservoirs 3 , 11 , 12 . It has been found that PV array alone, or with the installation of aerators and/or underwater ultrasound systems, reduces the proliferation of algal blooms in waters with many nutrients, thus preventing staining and the bad taste of the water 13 .

Animal life

Fishing farms can be introduced in the PISF channels as a new aquaculture activity 3 . In ponds containing fish, no harmful effects on aquatic fauna have been reported due to shading caused by PV arrays. On the contrary, in at least one case, in the lake with fish (mainly carp), it was found that fish prefer shaded water with little ripple under the PV array. There was a great increase of the shoal in the region of the PV arrays making the surroundings a very popular place for fishermen 8 .

It has been observed that the coverage of the already existing flooded areas did not alter the migratory habits and migratory routes of the birds in the region. However, as floating PV installations are recent, it is necessary to observe the local biome of each installation to identify and mitigate any environmental impacts. There are no conclusive studies on the environmental impacts caused by photovoltaic installations. The research into environmental impacts must be continuous, thorough, and comprehensive. Likewise, the socioeconomic impacts of such projects must be evaluated.

PISF transposition system description

The whole system includes, besides the artificial open-top channels and pumping stations, the natural waterways of the rivers and reservoirs. Artificial channels comprise 5% of the free water surface, riverbeds 5%, and reservoirs 90% 1 .

At the current stage, all artificial system sections are operational and reach the most distant users. Retrospectively looking, civil works were completed in 2017 (East) and 2020 (North) 14 , 15 , 16 . Built power infrastructure delivers to 9 pumping stations and substations but must still be fully equipped. Only the two installed pumping systems attend the current flow rates in each station; without a standby pump.

The channels

The channels are artificial constructions of trapezoidal shape with typical cross-sections as illustrated in Fig. 2 . The parallel edges of the channel allow it to be used as a support base for metal structures perpendicular to the channel, which can accommodate the PV modules.

Typical channel cross-section. The size parameters U is the upper edge dimension and b is the bottom edge of the channel. The water blade with a deep of Y results in the water surface with an extension \(\underline{B}\) .

At the project location’s latitude, the ideal slope of the panels is 9 degrees (almost horizontal), which requires a short distance to avoid shading one line of the panel over the next, reducing the space between the lines and allowing for more compactness. The inclination of the modules must be such that it allows for the flow of water used in the cleaning of the modules. Typically 10–15 degrees allow for adequate drainage. At this latitude, there are no great advantages in using vertical solar tracking systems, which reduces installation, as well as maintenance, costs.

On the Northern Axis of the project, the channels are naturally oriented to the north, so that the channel cross section accommodates the PV arrays in the ideal orientation. On the Eastern Axis, the modules can also be mounted on structures transverse to the channel direction, in-spite they will not be oriented to the north.

The flowchart Fig. 3 shows the structure of the Northern Axis of the PISF: the pumping stations, the current flow rates in each stretch, the position of the reservoirs, and the water consumption points ( \(D_{UF}\) ) with their respective outflows. However, these outflows were leveled to attend only 85% of current water demand at the delivery points 17 .

The Northern Axis schematic diagram.        Source: Trajano Jr.  1 .

The project schedule was divided into 3 stages called “Goals”. The channels of the first stage of the North Axis (Goal 1 North), up to the Jati Reservoir, have 20  m upper-edge and an extension of 110  km as described in Table  1 .

Goal 2 and Goal 3 channels are smaller but longer, totaling 160  km up to São Gonçalo Reservoir at Piranhas River.

Table  2 describes the Eastern Axis, which is also scheduled in three goals, distinct in shape and construction schedule. The channels of Goal 1 East, up to the Copiti Reservoir, have 15  m upper edge and an extension of 93.4  km including pumping stations EBV-01 to 04, and they were built first. Goal 2 East and Goal 3 East channels have 10  m upper-edge and an extension of 88  km . These channels, the two pumping stations, EBV-05 and 06, and the Monteiro tunnel were built later. Eastern Axis is complete and operational.

The top edge area of all channel extensions totals 6.313.495  \(m^{2}\) . The channel’s upper-edge design can easily support steel structures for PV coverage. All the 450  km of the open channels extension are ready to receive PV arrays.

Pumping stations

The three pumping stations EB-1, EB-2, and EB-3 on the North Axis are designed for maximum future capacity and can accommodate up to 8 pumps each. In the current phase, to meet the project’s flow rate, only 2 pumps were installed at each station. The pumps used in EB-1 (Fig. 4 ) are KSB model SEZ 15-110/2 driven by 5,500  kW / 6,900  V electric motors 18 . At EB-2 the pumps have 10  MW motors; on EB-3 motors are 2.7  MW . Altogether, the 3 pumping stations on the North Axis require 36.5  MW in the current stage, and 146  MW in the final phase of the project.

Pumping station EB-1.    Source: Brazil---Ministry of National Integration/Disclosure.

On the East Axis, the flow rates are lower. About 60% of flow rates in the North Axis as foreseen in ANA–Resolution No 632018. Water must be pumped to cover greater unevenness, reaching a total of 332 m. This will be done in six steps, so 6 pumping stations, EBV-1 to 6, are built. Each of these will have 4 pumps to reach the final stage flow rate; in the first stage – only 2 pumps at each station.

The power of the designed pumps is 5.3  MW , 3.7  MW , 5.5  MW , 5.3  MW , 2.2  MW , and 3.4  MW , respectively. Altogether, pumping stations on the East Axis require 51  MW in the current stage, and 102  MW in the final stage of the project.

To supply power to all the pumps, new 230  kV transmission lines were designed and built to serve the final project’s stage. The 270  km of high-voltage power lines are connected to the Paulo Afonso Hydroelectric Power Plants Complex which contains a total of 23 turbo generators with a nominal installed capacity of 4.28  GW 19 . Nine substations reduce the tension to 6.9  kV , as required by the pumps’ electric motors.

Regional meteorological and social characteristics

The Northeast hinterland is the driest region of Brazil 20 with precipitation not exceeding 400mm per year in different locations and, it is, therefore, susceptible to desertification 21 . Semiarid regions are subject to water shortages and soil degradation in such places is likely to increase with climate change 22 . The watercourses are generally formed by temporary rivers (also called intermittent), except for the São Francisco River.

According to the United Nations Convention to Combat Desertification 23 , the determination of an area susceptible to desertification can be carried out through the aridity index (AI).

This index corresponds to the ratio between precipitation ( mm ) and potential evapotranspiration ( mm ), the latter being defined as the amount of water that could evaporate or transpire from a vegetated surface due to atmospheric influence 24 , 25 .

When the AI is between 0.2 and 0.5 the climate is characterized as Semiarid (BSh in Köppen climate classification) 26 ; what is the situation in large areas of the Northeast hinterland as shown in Fig. 5 which covers all of PISF’s region. The semiarid region of Northeast Brazil covers 969,589  \(km^2\) 27 .

Northeast Brazil aridity map, showing the PISF region in which AI is 1.0 and below. Source: Adapted by the authors from Reboita et al. 20 .

The Brazilian Semiarid is the most populated semiarid area in the world and, due to climate adversities, associated with other historical, geographical, and political factors, that date back hundreds of years; it houses the poorest part of the Brazilian population, with the occurrence of serious social problems 27 , 28 .

This region has one of the highest rates of social and economic inequality in Brazil. Problems such as hunger, poor distribution of income, poverty, and rural exodus are recurrent, above all, in the interior cities of this deprived region. This has caused large-scale migrations.

In this area, which covers the eastern portion of Piauí (PI) and most of the states of Ceará (CE), Bahia (BA), Sergipe (SE), Pernambuco (PE), Paraíba (PB), Alagoas (AL) and Rio Grande do Norte (RN), the main economic practice is extensive livestock.

Therefore, in this region, known as the “Polygon of Drought”, the problem of lack of rain has been known and documented since the 16th century. It was officially first created in 1936. By the 1946 Constitution, Article198, the execution of a defense plan against the effects of the so-called drought in the Northeast was regulated and disciplined. The legal framework for the creation of this area was finally instituted in 1968, through the Brazilian government Act No 63,778 29 .

Contrary to popular belief, the northeastern drought is not solely a natural phenomenon. While seasonal shifts in rainfall patterns and occasional delays in precipitation play a role, several factors contribute to its severity and persistence. This usually happens when the Inter-tropical Convergence Zone (ITCZ) does not reach the northeastern region in the period between summer and autumn. Factors such as La Niña and the burning of native vegetation also directly affect the region’s drought regime.

According to the WMO, La Niña will continue to affect temperature and precipitation patterns and exacerbate droughts and floods in different parts of the world. Terrestrial water storage (TWS) of the São Francisco river basin exhibits a gradual decrease, with 2021 being the year with the lowest TWS between 2002 and 2021 30 . For the first time this century, the La Niña phenomenon will last for three consecutive years.

The year 2021 was ranked between the fifth and seventh warmest year on record, with the global annual mean temperature of 1.11  \(\pm 0.13 ^\circ\) C above the 1850–1900 pre-industrial average, despite prevailing La Niña conditions 31 . The last ten years were the warmest on record, with rising sea levels and warming oceans accelerating. The continuity of La Niña prolongs the conditions of drought and flooding in the affected regions it caused the longest and most severe drought in recent history.

Drought periods directly affect the weather of this area. Exerting pressure on water, agriculture, and food supply, climate change is having devastating consequences for arid regions 32 . The global warming scenario points to prolonged and severe drought periods 33 , 34 , 35 , which will lead to prolonged and greater suffering for the population of this arid region. Drought periods make water supply to this region of vital importance.

PV power potential

The Northeast region has the largest solar energy resource, on average 5,9  \(kWh/m^{2}\) , and presents the smallest inter-annual variability (between 5.7 and 6.1  \(kWh/m^{2}\) ) 36 . The high solar radiation encourages using PV as a power source. Fig. 6 illustrates the solar potential of the São Francisco River valley and highlights the PISF area.

Solar potential of all the São Francisco Valley extension, highlighting the region of the PISF water transposition project. Source: Adapted by the authors from globalsolaratlas.info.

Traditional PV arrays installed on land require roughly 3.3  ha / MWp . This is because spacing is necessary to prevent shading of one row of panels by the next, and to allow for access for cleaning and maintenance. In contrast, floating PV installations are denser and can occupy less area than their terrestrial counterparts. Floating PV footprint is smaller than on land PV arrays In this article the \(\mu _{PV} = 10\,{m^2/kWp} = 1\,{MWp/ha}\) was considered for both 37 , 38 .

Channels top can be fully occupied by PV modules separated only by walkways between the lines to allow maintenance, and some required access to the channel itself. Those why the considered \(\mu _{PV}\) value is conservative 39 , 40 , 41 , 42 and is used to safely estimate channels and free water coverage area by PV panels. Current solar technologies allows \(\mu _{PV} = 7.5\,{m^2/kWp}\) . When detailing the channel coverage project, engineering design can reach this lower occupation factor and increase the power installed.

Results and discussion

Solar radiation.

The seasonal profile for PISF’s location is in Fig. 7 . According to monthly data from the Global Solar Atlas, at EB-1 (8.526978 S; 39.459736 W) the annual average of daily radiation is 5.384  \(kWh/m^{2}.day\) . The peak occurs in October and reaches 6.785  \(kWh/m^{2}.day\) .

Local radiation profile at Pumping station EB-1. Source: Elaborated by the authors using the data of the Global Solar Atlas 43 .

Feasibility of using PV energy

To meet the power requirements of the 2 pumps installed in each pumping station of the Northern Axis, 365,000  \(m^2\) of solar panels are required. Considering the typical upper edge width of 20  m of the channels close to the pumping stations, it is necessary to cover an 18  km channel extension in the vicinity of the three pumping stations (can be upstream or downstream). This will reduce transmission losses and minimize the cost of cabling. It is necessary to cover less than 17% of the Goal-1-North 110  km length of the built channels. To meet the final (maximum) capacity of the project, this percentage rises to 68%. However, Goals 2 and 3 of the northern axis have an additional 160  km of channels with an upper edge width of 12 and 10  m .

At the Eastern Axis, with channels extension of 201  km , to meet the power requirements of the 2 pumps already installed in each of the 6 operating pumping stations, 508,000  \(m^2\) of solar panels are required. As the typical upper edge width of 15  m of the channels, it is necessary to cover 34  km of channels which is circa 21%. This percentage rises to 42% to meet the final stage of the project.

The PV array will cover the entire channel, shading the water regardless of the flow and depth of the water. For this purpose, the Indian model, with the solar panels mounted on a metallic structure supported on the upper edges of the channel, may be the most suitable. The PV installations can reduce by 25% the daily consumption of the grid energy to power the pumps.

This design concept was successfully used to cover 750  m of an irrigation channel in Narmada, in the state of Gujarat, India, 2013, reducing water loss through evaporation and generating 1  MW 44 , p.19. The same concept of installation, including the substation, can be observed in an article regarding megawatt-scale canal-top solar power plants bid in India, with a photo of the area view 45 .

California, USA, grapples with comparable issues concerning its water channels. The region experiences severe periodic droughts, exacerbated by climate change and excessive water consumption. These factors wreak havoc on the region’s water supply. Open irrigation channels further exacerbate the problem by allowing precious water to evaporate. Despite this, the intricate network of channels remains crucial for delivering water throughout California. The channels snake their way through the Central Valley, transporting water to irrigate crops. The sheer scale of this system, spanning 6,500  km , presents an opportunity for covering the aqueducts with PV systems. This emerging technology addresses the interconnected water-energy-food nexus, offering a promising response to the challenges faced by California’s water infrastructure. Researchers from UC Santa Cruz and UC Merced found that “...it makes sense to cover channels with PV panels because renewable energy and water conservation are a win-win project... 46 ...Energy and water co-benefits from covering channels with solar panels” 46 , 47 .

Balram and Narayan Bhardwaj suggested the use of micro-hydrokinetic turbines combined with PV panels chancels’ to increase power generation. PV panels on the topside capture the sun’s energy, while micro-hydrokinetic turbines on the bottom capture hydro-power from the flowing water 48 . This combination increases the power output of both the solar and hydro components. The channel-spanning infrastructure to support the PV arrays also serves as a solid foundation for the hydrokinetic turbine arrays 48 , 49 .

Taboada et al. research in Northern Chile, at Antofagasta in the Atacama Desert, found that the water evaporation reduction in a pond with floating covers in their region was at least 90%, compared to an uncovered pond 50 . Recent studies pointed to an average reduction of the evaporation from open water bodies in studied semi-arid regions up to 60% 10 . The authors consider that these rates may be too high for the PISF project. A field investigation on PISF channels should be done to accurate the regional value of the evaporation reduction rate.

Abd-El-Hamid et al. have been researching the evaporation loss of Lake Nasser, in Egypt. Their study suggests the use of floating PV arrays to cover parts of the lake to reduce water losses due to evaporation. They found that covering the very shallow parts of the water body, up to 1.0  m depth, will provide the highest water saving 51 .

Pringle, Handler and Pearce suggested that when covering the water surface with PV arrays, a reduction of 20% to 25% in the loss of water through evaporation is expected 3 .

PISF’s artificial channels are ideal for this solution. The surface that can be covered by PV arrays on the totality of the PISF channels is about 6.5  \({km^{2}}\) (sum of tables 1 and 2). If considering the uncovered spaces due to engineering needs, a surface area \((S_{PV})\) of at least 5  \({km^{2}}\) is available for PV installations. If the entire length of the channels is covered, the installed PV power will be 500  MWp , providing solar energy to the pumping stations and grid during times of significant radiation (day). The energy generated by these facilities is obtained from Eq. ( 3 ):  \(E_{PV} = 365 \times \overline{H} \times \eta _{PV} \times PR \times {S_{PV}} = 365 \times {5.384} \times {0.15} \times {0.8} \times {5} = 1,180\,{GWh}\) . Although the combination of PV and hydrokinetic turbines technology was proposed for canal-top projects, the design can be modified and adapted to the floating solar concept environment 48 increasing the energy produced.

Water savings can range from 15,000 to 20,000  \(m^3/year\) for each installed 1  MWp 4 . PV power plants of 500  MWp will save: \({500\times [15,000~to~20,000]}/{365}\) = [20,548–27,397]  \({m^3_{Water}/day}\) . As the PISF region is very hot, the tendency is to stay at the top of the referenced range of values.

Despite representing only 5% of the overall water surface, artificial channels experience higher water loss compared to natural waterways, contributing to a staggering 16% of the total loss. Covering these channels is crucial to reducing water loss through evaporation.

According to the National Water Agency (ANA), water losses in the northern axis channels amount to 800  L / s 17 , while the eastern axis channels lose 500  L / s 52 . This totals 1,300  L / s . Covering the channels with solar panels offers the potential to avoid up to 25% of this loss. This significant reduction translates to a daily saving of 1,000 water truck trips, each carrying 25  \({m^3}\) of water. The implementation of this solution could significantly improve water conservation efforts, reduce reliance on water trucks, and contribute to a more sustainable water management system.

While the artificial channels of PISF account for only 5% of its total water surface area, the natural riverbeds make up a similar proportion, together covering 10% of the system. The remaining 90% of the water surface area belongs to reservoirs, ponds, dams, lakes, and lagoons ( 1 . For these large water bodies, a different approach to reducing water evaporation is more suitable: floating photovoltaic islands.

There is no incompatibility between the 2 models of PV plants described, which can be combined according to engineering design conveniences.

Floating PV installations

This method involves installing solar panels on floats and creating platforms partially covering the water surface. This approach generates clean energy while simultaneously reducing evaporation losses through evaporation in the regions covered by the solar panels 53 , contributing to increased water availability for distribution to consumption points 54 . By utilizing the same water surface for both energy generation and water conservation, this approach optimizes the use of available resources in terms of a multi-functional use of water bodies.

Studies have shown that floating systems, compared with suspended systems, have a higher yield in terms of evaporation reduction 55 , 56 . Floating PV also takes advantage of the water’s cooling effect and can use horizontal solar tracking to improve its efficiency 40 . Researchers pointed out that the average power production of floating PV systems is up to 15% higher than traditional on-land installations due to the lower working temperature 57 .

Floating PV systems already exist in Brazil, installed in water reservoirs and even close to hydroelectric power plants dams. At the Figueiredo das Lages farm, in Cristalina-GO, a 300  kWp floating PV array was installed in 2016 to reduce water evaporation and generate electricity, view photocopy 58 . This concept is used in several similar installations all over the world and is expanding fast 59 . In 2018, the floating PV technology surpassed the 1,000  MWp mark 60 . In 2022 the total installed capacity exceeded 4  GWp 61 .

The Sobradinho hydroelectric power plant is located in the same region as the PISF. The meteorological conditions are the same for both of them. The PV generation potential and the annual energy yield of this region are the best in Brazil’s territory. Power generation facilities up to 5.0  MW are regulated by a specific distributed generation (DG) legislation in Brazil. Larger facilities require new regulations. The first stage of Sobradinho’s 5.0  MWp floating PV power plant R &D project, a 1.0  MWp floating array (Fig. 8 ) started operation in 2019. Data obtained from this plant can lead to accurate and precise design parameters for the suggested PISF PV project 62 .

Floating PV Power Plant at Sobradinho hydroelectric power plant reservoir.to Springer Nature exclusively under CC BY SA for this study 63 .

Capital expenditure estimation

The Capital Expenditure (CAPEX) of a PV power plant in Brazil ranges between 2,500 and 5,000  BRL / kWp , with a reference CAPEX of 3,800  BRL / kWp (base 2021) 64 . These values were validated by Enel Green Power, which built the ground-mounted PV plant Bom Jesus da Lapa, in the region close to PISF, with a rated power of 80  MWp , running since 2017, with a declared CAPEX of 3,750  BRL / kWp .

The CAPEX of PV-FPP is slightly higher, owing chiefly to the need for floats, moorings, and more resilient electrical components. The cost of floats is expected to drop over time, however, owing to better economies of scale 60 . The CAPEX estimation of a PV-FPP in Brazil ranges between 3,800 and 6,500  BRL / kWp , with an average value of 5,000  BRL / kWp 64 .

A study based on January 2019 prices pointed to a CAPEX of 4,415  BRL / kWp and a payback of 10 years. However, when considering the investment in a floating PV system to avoid water supply to the population of the arid regions of the Northeastern hinterland by diesel-driven trucks, the payback is only 4 years 54 .

Channels coverage requires additional steel structure than a land installation but does not require land acquisition. The estimated CAPEX will be in the range between ground-mounted PV and PV-FPP, circa 4,500  BRL / kWp .

PV systems can be implemented in stages and come into operation as soon as each stage is completed, easily adapted to the budget and schedule. The final CAPEX of PISF was updated to 18 billion BRL 65 . The cost of the electric power to feed all the pumps is around 500 million BRLyear. The capital to implement coverage of the entire length of the channels with PV systems is estimated at an additional 2.0 billion BRL (11% of the transposition project’s CAPEX or 4 years of electricity cost). To convert amounts to US Dollars, a general rate of (5.00  BRL /1.00  USD ) may apply.

The lack of water has been a major obstacle to the human development of millions of Brazilians in the 21st century 6 . The Integration Project offers an efficient and structured solution to increase the water supply, providing relief to a population and an entire region suffering from drought. The primary objective of this transposition project is to supply the population with water. By reducing evaporation losses, the project will ensure greater water availability at the destination with the same amount of energy used in pumping, effectively improving the system’s energy efficiency 66 , 67 , 68 , 69 , 70 .

The use of free water surfaces to install floating PV arrays is a modern and sustainable C-free solution in the water-energy nexus. Electric vehicles of the maintenance fleet will help further reduce the project’s carbon footprint, making it more sustainable and environmentally friendly. Water savings of this solution will enhance the PISF’s main goals of supplying the deprived Northeast population, improving their quality of life.

To meet the power demand of the current stage pumping stations, PV systems must cover less than 20% of the channels. However, to reduce the evaporation loss, it is desirable to cover the entire length of the channels saving a daily additional 25,000  \(m^3_{Water}\) to supply the population, and, generating 1,200 GWh yearly

The energy surplus generated from the entire coverage of the channels can be stored in battery stations (BESS) to compensate for the solar inconsistency and variability and ensure energy quality. This will contribute to supply the demand of low/no radiation time. Otherwise, this energy surplus will feed the electric grid to supply the National Integrated System (SIN), which contributes to mitigating the newest peak of demand that occurs in the summer between 10 a.m. and 4 p.m. according to data from the National Electric System Operator (ONS) 71 . This will avoid the use of thermal power plants that produce greenhouse gases and increase electricity costs, in addition to being in line with the Ministry of Mines and Energy’s ten-year planning 72 which intends to reach the installed solar power plants capacity of 14.5  \(\overline{GW}\) in 2030 (4.5% of the country’s electric matrix), and with Brazil’s GHG emission reduction commitments 73 at the United Nations Conferences on Climate Change (UNFCCC), COP21 (Paris) and after 74 .

The concept of “solar canals” has been gaining traction around the world as climate change increases the risk of drought in many water-scarce regions 75 . The technology for PV installations is current and available. The scale is technically feasible, as India has shown 76 .

Final thoughts

Evaluating the local solar radiation and environmental impacts, the same technology can be applied worldwide to irrigation channels in places where water is lost through evaporation. Asia already applies coverage of water channels, lakes, and, ponds with solar panels. Other continents, especially Africa, South America, and the Pacific Islands can also take advantage of this technology in the water-energy-food nexus, benefiting the local population. Despite the intensive capital costs required, the saving of water and power makes these projects feasible. The waterways would, in a sense, make PV panels water-cooled, boosting their efficiency. Energy and water co-benefits from covering channels with PV panels. Solar-paneling channels would not only produce renewable energy, it would run the water system itself 46 , 47 . These projects are fully aligned to the United Nations Development Programme (UNDP) –2030 Agenda for Sustainable Development–, Sustainable Development Goals (SDG) Nr. 6, 7, 8 and 9 77 , 78 . The use of PV-FPP will reduce emissions of \({CO_{2}}\) , and other GHG, by electricity generation from fossil fuels, helping to combat climate changes and the impacts of the global warming process; SDG Nr. 13 (Climate Action). As the atmospheric pollution is only getting worse, it requires application development or PV expansion to avoid unnecessary environmental impacts. This does not need direct funding, but a suitable policy 79 that serves humanity 80 .

Data availability

All data generated or analysed during this study are included in this published article.

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Acknowledgements

This work was carried out with the support of the Coordination of Improvement of Higher Education Personnel---Brazil (CAPES). The first author would like to thank the Graduate Academic Program on Energy of The Federal University of ABC (UFABC) which has provided the knowledge necessary for this research development. The study also gained significant contributions from the University of Turku’s Virtual Training Center project outage for practical management deployment, concluding the project great with thanks.

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Review article, implementation of water energy food-health nexus in a climate constrained world: a review for south africa.

• 1 Council for Scientific and Industrial Research (CSIR), Climate Services Research Group, Pretoria, South Africa
• 2 Sustainable and Smart Cities and Regions Research Unit, Department of Urban and Regional Planning, Faculty of Engineering and Built Environment, South Africa School for Climate Studies, University of Johannesburg, Johannesburg, South Africa
• 3 Department of Agricultural Economics, University of Stellenbosch, Stellenbosch, South Africa
• 4 Department of Geography and Environmental Sciences, University of Venda, Thohoyandou, South Africa
• 5 Department of Botany and Zoology, School of Climate Studies, University of Stellenbosch, Stellenbosch, South Africa

In recent years, the Water-Energy-Food (WEF) nexus has gained significant attention in global research. Spatial inequality in water-energy-food security (WEF) and its impact on public health and how this is affected by climate change remains a grand adaptation challenge. South Africa is extremely vulnerable and exposed to the impacts of climate change due to its socio-economic and environmental context. While alternative nexus types have garnered interest, this paper pioneers an extension of the conventional WEF framework to encompass health, giving rise to the Water-Energy-Food-Health (WEF-H) nexus. Despite a plethora of WEF nexus studies focused on South Africa, a substantial knowledge gap persists due to the lack of a comprehensive overview of the enablers and barriers to realizing the WEF-H nexus. South Africa boasts diverse policies related to water, energy, food, and health; however, their alignment remains an ongoing challenge. This study seeks to bridge this critical gap by conducting an exhaustive review of existing literature. Its primary aim is to delve into the intricate mechanisms that either facilitate or impede the actualization of the WEF-H nexus in South Africa. By synthesizing insights from a wide array of literature sources, this research strives to illuminate the challenges and opportunities stemming from the integration of health considerations into the established WEF nexus framework. This exploration holds immense significance, not only for unraveling the multifaceted interactions between these pivotal sectors but also for guiding policy development and decision-making processes in South Africa towards a more holistic and sustainable approach to resource management.

1 Introduction

Despite three decades of democracy, South Africa still struggles with the legacy of apartheid, including extreme inequality across racial and regional lines ( Klug, 2021 ), widening gulfs between the rich and poor ( Naidoo, 2005 ; Sibanda and Batisai, 2021 ) compounded with increased frequency of climate-induced hazards. The 1994 transition to majority rule in South Africa aimed to reduce socio-economic inequality, expand basic services, and embrace human rights principles as the foundation of constitutional solutions ( Klug, 2021 ). Access to water, food, health, and energy services are basic human rights, but the struggle for these rights continues to echo the popular struggles of the apartheid era. The South African government is committed to eliminating poverty and reducing inequality by 2030, as set out in its key national policy documents, e.g., National Development Plan 2030 ( NPC, 2011 ) and National Climate Change Response Policy (NCCRP) ( DEA, 2011 ) as well as the international agenda for Sustainable Development Goals (SDGs) to which the government has subscribed. Despite the government’s valiant efforts, many South Africans continue to face socio-economic challenges and the ramifications of climate change ( Naidoo, 2005 ; Sibanda and Batisai, 2021 ). This reality is particularly pronounced among the country’s black African population.

Like many developing countries, South Africa faces the challenge of balancing economic growth with environmental sustainability, what Simpson coined “reconciling growth with planetary boundaries” ( Simpson and Jewitt, 2019 ). This means developing the economy in a way that is equitable, inclusive, and does not irreversibly damage renewable resources or fail to realize the full potential of non-renewable resources. However, South Africa’s political economy has tended to prioritise an economic approach that transfers problems to a wide range of sectors. For example, mining rights often trump conservation of strategic water resource areas, agriculture lands and even human health considerations. As a result, tensions are growing between the increasing demand for, and use of natural resources (e.g., water, land, and energy) to support development and the availability and quality of those resources.

Coupled with its developmental challenges, the country is also water-stressed, with climate change ( Nhamo et al., 2020 ) further compounding existing socio-economic challenges. Escalating food prices ( Simpson and Jewitt, 2019 ) are leaving a large portion of the population highly food insecure, unable to meet their basic nutritional needs. Even more urgent and complex is the issue of the ailing energy system. Eskom, the national power utility has failed to meet the energy demand resulting in frequent power outages ( Baker and Phillips, 2019 ; International Energy Agency, 2022 ) and increased rationing of the available energy ( Lawrence, 2020 ).

South Africa has many policies related to water, food, and energy, which aim to make these sectors more sustainable. However, many stakeholders are increasingly recognizing the importance of managing the complex interactions between water, energy and food (WEF). The WEF nexus, an approach that considers these three sectors together, has been suggested as a governance solution to complex resource management challenges ( Srigiri and Dombrowsky, 2022 ). This paper examines the implementation of the WEF-H nexus in a country case study, with a focus on the key bottlenecks and enablers. The paper acknowledges that more than a decade after the introduction of the WEF Nexus as a governance ( Keskinen et al., 2016 ), analytical ( Nhamo et al., 2020 ) and ideological tool, the transition from “nexus thinking” to “nexus doing” remains essential to foster appropriate policy development, effective decision-making and practical implementation, in the context of water, energy, food, and health interlinkages.

The paper explores developments in the WEF-H nexus through an extensive literature review, unpacking its complexity and challenges within the South African context, and examining the key ingredients for successful implementation.

2 Understanding the nexus concept

The term “nexus” is central to the WEF-H Nexus, and it refers to a polycentric approach to problem solving ( Srigiri and Dombrowsky, 2022 ). As such, the nexus concept is a useful framework ( Keskinen et al., 2016 ) for action that brings together multiple actors and institutions at different levels of governance to address complex challenges. It is both an analytical tool and a discourse centred on the theory of polycentricity ( Thiel, 2016 ) and polycentric governance ( Ostrom, 2010 ) which means that power and decision-making are distributed across multiple centres.

In simpler terms, a nexus approach is a systems-based way of thinking about complex problems by considering how different sectors are connected and how decisions made in one sector can impact on others. This may be especially useful for identifying the inter-relatedness and interdependencies between sectors when making decisions about projects, strategies, policies and investment options in complex socio-environmental systems ( DeLaurentis and Callaway, 2004 ). It aims to integrate research, management and governance across sectors and scales. The nexus approach assumes that there are biophysical and environmental limits to the degree to which resources can be exploited or pollutants can be absorbed, and that exceeding these limits will have potentially catastrophic impacts, either now or in the future.

Moreover, it is understood that there are complex feedbacks within and between sectors ( Mutanga et al., 2016 ), often resulting in non-linear responses, and tipping points beyond which systems cannot easily recover ( Cabrera et al., 2008 ). The nexus approach allows for a more holistic understanding of (un-)intended consequences of policies, technologies and practices whilst highlighting areas of opportunity for further exploration ( Trist, 1981 ; Mutanga et al., 2016 ). It aims to enhance resource-use efficiency (resource-use getting more from less) and political cohesion by reducing resource trade-offs and increasing synergies. The nexus concept needs to be interdisciplinary and transdisciplinary, accepting a plurality of views ( Geels, 2004 ). It is also participatory, requiring stakeholders to engage with researchers in jointly deriving potential solutions. Given the above dimensions, resource-use remains clear that no single definition can be used to define nexus and its applications, it remains an evolving concept. What is clear though is that it forms the basis within which the WEF nexus is defined and understood.

3 The water-energy-food-health (WEF-H) nexus approach

The Water-Energy-Food-Health (WEF-H) Nexus is a complex concept with no single agreed-upon definition or framework. It is often used to describe the interconnectedness of these four sectors, and how challenges in one sector can have cascading impacts on the others ( Rasul and Sharma, 2016 ). The number of sectors included in the Nexus can vary, depending on the discipline or perspective and can sometimes add additional lenses such as livelihoods, ecosystems, and climate change ( Keskinen et al., 2016 ). For example, those in the water sector may refer to the Nexus as WEF, while those in the energy sector may refer to it as EWF. The agriculture sector may define it as FEW, and the health sector may add the ‘H’ ( Nhamo et al., 2020 ). This lack of common understanding can make it difficult to collaborate and develop effective policies and solutions.

Despite the lack of consensus on a definition, the WEF-H Nexus is a useful concept for understanding the complex challenges facing our world. It can be used as an analytical tool, a conceptual framework, or a discourse ( Keskinen et al., 2016 ). Instead of passively acknowledging the existence of the WEF-H nexus, this paper argues that it is a critical driver of resilience in both our economy and society. Recognizing its interconnectedness demands proactive measures – not just awareness, but concrete policies and actions. By effectively managing this complex system, we can harness its synergies and mitigate challenges, ensuring the WEF-H nexus becomes a potent force for resilience in the face of interconnected water, energy, food, and health concerns.

Nexus studies equip us with the knowledge and tools to tackle complex challenges head-on. By delving into resource efficiency, institutional dynamics, and policy integration, they provide a roadmap for action through methods like integrated models and stakeholder engagement. The WEF-H nexus is not just a concept; it's a powerful framework for shaping a sustainable future.

For example, it enables consideration of ways to:

i. Address energy security without impacting further on food or water resources.

ii. Improve water security without increasing the energy burden of water management.

iii. Create a more circular system by integrating food production with water and energy utilization. Wastewater can be treated and reused for irrigation, renewable energy can power agricultural processes, and food waste can be converted into biofuels or compost.

iv. Encourage sustainable food production practices that prioritize nutrient-rich crops and diversified diets which can contribute to improved public health and reduced malnutrition.

v. Create new green jobs in renewable energy, resource recovery, and precision agriculture, thereby meeting job creation ambitions in a sluggish agricultural economy without overextending water and energy resources.

The four most important interfaces in the water-energy-food-health (WEF-H) nexus are:

• Water which plays a vital role in both food and energy production, and for sustaining the ecosystems that support agriculture and other economic activities that are critical for food security.

• Energy, which is required for food production (especially irrigation) and for water supply, including the extraction, purification, and distribution of water.

• The role of food production as a consumer of land, energy, and water as well as their interlinkage with health.

• Health which is an intrinsic component of the WEF-H nexus, as the wellbeing of individuals is intricately linked to the quality and availability of water, the energy required for sustenance, and the nutritional aspects of food production. Recognition of the interconnections between addressing the challenges and opportunities within this interconnected system.

Agriculture, which is responsible for growing food, is a major user of water (more than 70% of all water use globally) and energy ( Rasul and Sharma, 2016 ). Agriculture and food production also affect the water sector through land degradation, changes in runoff, and disruption of groundwater discharge (Shinde, 2017). Recognizing the intricate connections within the Water-Energy-Food-Health (WEF-H) nexus is paramount. Health, as a crucial facet of this nexus, is intricately linked to the availability and quality of water, the energy required for sustenance, and the nutritional aspects of food production. A holistic understanding of these interdependencies is essential for comprehensive and sustainable management within the WEF-H nexus.

4 Taxonomy of nexus approaches

According to Bian & Liu, (2021) , there are four globally recognized nexus types:

• Water-energy: This nexus focuses on the interconnectedness of water and energy systems. For example, energy production often requires large amounts of water for cooling, while water distribution and treatment require energy ( Wilson et al., 2021 ).

• Water-food: This nexus focuses on the connections between water resources and agriculture. Agriculture, particularly irrigation, is a major consumer of water resources. Consequently, fluctuations in water availability directly impact food production.

• Water-energy-food: This nexus adopts a holistic approach, bringing together the three core elements of water, energy, and food. It underscores the need for integrated planning and management, recognizing the interconnectedness and interdependence of these essential domains.

• Water-energy and climate: In this context, the nexus signifies the interplay between water, energy, and climate factors. It acknowledges the substantial influence of climate change on water resources, energy production, and food security. For instance, altered precipitation patterns can disrupt water availability, and extreme weather events have the potential to damage energy infrastructure and disrupt food supply chains. The discussion aims to clarify that the nexus represents the combination of these sectors, emphasizing the importance of a comprehensive understanding and strategic planning within the broader WEF-H context.

In recent years, additional nexus types have emerged:

• The Water-energy-food-ecosystems (WEFE) nexus: This nexus recognizes the pivotal role of ecosystems in shaping and sustaining the interconnections among water, energy, and food systems. Ecosystems provide indispensable services, including clean water, pollination, climate regulation, and biodiversity, which underpin the functionality of water, energy, and food systems ( De Roo et al., 2021 ). The WEFE nexus highlights the profound interdependence between ecosystems and the essential sectors of water, energy, and food. It emphasises the need for holistic, integrated resource management approaches that recognize the intrinsic value of ecosystems in sustaining human wellbeing and promoting environmental resilience.

• Nuwayhid and Mohtar, 2022 contends that Water-Energy-Food-Health (WEF-H) nexus is a comprehensive framework that explores the intricate relationships between water resources, energy production, food systems, and public health. Unlike the WEFE which advances ecosystems as a critical physical component this nexus advances the health wellbeing. Equally it recognizes that changes in one domain can have significant impacts on the others though with an inherent interlinkage between physical components and human wellbeing. For instance, water is crucial for human survival and agricultural production, while energy is essential for water treatment and food processing. Similarly, food quality and availability directly affect public health. This approach underscores the need for integrated, sustainable strategies in resource management and policymaking, emphasizing that decisions in one sector can have far-reaching consequences for the others. By embracing the WEF-H nexus, stakeholders can better address complex challenges related to resource scarcity, environmental sustainability, and community wellbeing through collaborative and innovative solutions refer to ( Figure 1 ).

• Another nexus type, the water-energy-food-biodiversity-health (WEFBH) nexus, encompasses the complex interdependencies between water utilization, energy generation, food supply chains, and environmental and public health ( Hirwa et al., 2021 ).

Figure 1 . WEF-H nexus adaptation framework.

The interrelationships between the nexuses are illustrated in Figure 1 . Essentially the framework for WEF-H Nexus not only captures the traditional WEF but encapsulates the health dimension as an equal sectoral lens to the nexus thus providing a holistic dimension. Policy framing is broadened to include issues around “healthy water,” “sustainable energy for health,” and “nutritious food for wellbeing.” Health metrics can be tracked alongside traditional WEF indicators to monitor the Nexus’s impact on health and identify areas needing improvement. Moreover, the nexus adaptation framework recognizes that the nexus is influenced by several exogenous factors including the impact of climate change, the policy sphere, institutional mechanisms as well as the financial mechanisms all of which have an inherent effect on each of the sectors identified in this nexus.

Building on the foundation of previous nexus typologies that excluded health, the Water-Energy-Food-Health (WEF-H) nexus is a powerful tool at the socio-political level. It can alleviate tensions caused by poor coordination among non-state actors and inadequate service provision by the state. The WEF-H nexus also presents a unique opportunity to shift the focus from governance challenges to community empowerment, fostering self-reliance and sustainability. This empowerment includes showcasing alternative livelihood possibilities.

Furthermore, the WEF-H nexus has the potential to bridge the gap created by inequitable partnerships, whether rooted in gender, wealth disparities, racial divides, educational levels, or social statuses which have become pervasive in South African society. The nexus approach can contribute to what we term “societal hope,” instilling a profound belief within communities that they can chart a course away from hopelessness, even in the face of governance inefficiencies and limited access to opportunities. The principles thereof illustrated in Figure 1 include environmental stewardship which advocates for investment in sustaining ecosystems services, social equity, resource use efficiency as well as the integrative perspective. These principles provide a foundation for merging effective pathways for successful implementation of NEXUS.

The adaptability of the Water-Energy-Food-Health (WEF-H) nexus, in contrast to other aspects of the economy, lies in its capacity to cater to communities with varying levels of knowledge and information. Unlike traditional economic frameworks, the WEF-H nexus is inherently versatile, offering a more inclusive approach that accommodates diverse communities. This adaptability stems from its comprehensive consideration of interconnected elements, allowing for nuanced solutions that address the complex and dynamic challenges present in the realms of water, energy, food, and health. By embracing a holistic perspective and fostering collaboration among stakeholders, including academics, civil society organizations, the private sector, government bodies, and international partners, the WEF-H nexus creates a platform that encourages innovation and technological advancements across multiple sectors and scales.

The WEF-H nexus holds the most promise for regions facing significant development gaps or struggling with complex socio-economic issues. It offers a powerful, unified approach to tackling these challenges and unlocking new opportunities. We characterize the opportunity presented by the WEF-H nexus as “extraordinary” due to its unique capacity to simultaneously address multiple facets of development challenges. The extraordinary nature lies in the nexus’s holistic approach, integrating water, energy, food, and health considerations. This all-encompassing strategy allows for comprehensive and interconnected solutions, offering a more effective and sustainable response to the complex socio-economic challenges and developmental hurdles that regions may face. The extraordinary nature of this opportunity is underscored by the potential for transformative and inclusive development outcomes, some of which are illustrated on Figure 1 as sustainable adaptation outcomes.

5 Key characteristics of the water-energy-food-health (WEF-H) nexus approach

The WEF-H nexus approach is inherently accessible and requires no demystification. It is conceptually straightforward and designed to be inclusive, catering to individuals of all backgrounds and levels of expertise. Recognizing that, for the general public, concepts such as the WEF nexus and the WEF-H nexus may benefit from some explanation, we emphasize the fundamental nature of this approach. It relates to some of the most essential human needs: water, energy, food, and health. In this paper, we have identified ten salient characteristics that are recognized by many scholars and in the literature on the WEF-H nexus, aiming to enhance clarity and promote a more inclusive understanding:

a. Multi-sectoral focus : The WEF-H approach unites a diverse range of stakeholders around a common set of goals, providing a platform for intentional and focused interaction. This cross-sectional coordination promotes convergence of perspectives and facilitates collaborative solutions.

b. Interconnectedness : WEF-H nexus broadens the understanding of interlinkages ( Simpson and Jewitt, 2019 ) recognizing the interdependencies ( Leck et al., 2015 ) between sectors i.e., water, food, and energy.

c. Social embeddedness. Beyond the physical/environmental connections of the nexus approach is the ability to recognize the social interactions among actors which may be referred to as social embeddedness interactions ( Srigiri and Dombrowsky, 2022 ). WEF thus considers the political and cognitive factors that are central to policy change within sectors ( Weitz et al., 2017 ).

d. Complexity : The multifaceted nature and interactions between and within different subsystems ( Mutanga et al., 2016 ) create complex dimensions that must be addressed. As a result, there is no one-size-fits-all model to deal with WEF-related issues ( Simpson and Jewitt, 2019 ). Instead, time-bound and place-bound solutions are encouraged.

e. Governance modes : Scholars studying the WEF nexus agree that integrative coordination across sectors, actors and levels of governance is essential, given the interconnected nature of the nexus ( Welsch et al., 2015 ). It is important to note that the WEF-H nexus approach does not seek to replace focus and attention on actions (planning, investments, implementation, etc.) related to related to water, energy, food and health. Rather, it aims to break down the siloed approach to managing these resources and promote coherent and balanced planning and implementation.

f. Holistic Approach : WEF-H nexus is a holistic approach that is consistent with well-established analytical frameworks such as Institutional analysis and development (IAD) framework ( Ostrom, 2010 ) value chain analysis ( Villamayor-Tomas et al., 2015 ), network of adjacent action situations (NAAS) ( Srigiri and Dombrowsky, 2022 ), multi-criteria decision-making models (MCDM) ( Kumar et al., 2017 ), Integrative Model ( Nhamo et al., 2020 ), as well as systems dynamics models ( Wen et al., 2022 ). All these tools share a common structure for solving complex decision and planning problems, but their application and impact vary across sectors.

g. Implementation : WEF-H nexus implementation is not an event, rather, it is a process that requires access to information about on-going plans and activities to ensure building-on and complementing those activities.

6 Barriers/bottlenecks for implementing nexus

The WEF-H is anchored in prioritizing the management of the four interconnected resources (water, energy, food, and health) in a sustainable way. However, implementing this nexus comes with different barriers and bottlenecks that hinder progress (detailed below and in Table 1 ).

Table 1 . Identified bottlenecks drawn from literature and recommendations for implementing WEF-H Nexus.

South Africa currently lacks a singular policy document that explicitly addresses the Water-Energy-Food-Health (WEF-H) nexus. This does not necessarily imply a lack of commitment but reflects the intricate task of navigating trade-offs and resource constraints. This, position reflects the broader global context where numerous nations are yet to formulate comprehensive policies on the WEF-H nexus. In many instances, the implementation of WEF-H activities remains imbalanced, with sectors such as water, energy, food, and health often managed in a sectoral or “silo” approach ( Nhamo et al., 2018 ). Despite the acknowledgment of the WEF-H nexus approach, these sectors frequently treat resources independently, guided by institutional structures ( Adom et al., 2022 ). The reluctance to enforce integrative policies is a complex challenge influenced by trade-offs embedded across sectors, particularly in resource-limited countries. South Africa, being a water-scarce nation, has ambitious plans to transition from coal-based to renewable energy, including hydropower ( Pegels, 2010 ; Ololade et al., 2017 ). This puts pressure on the water sector which has to prioritise maintaining the supply of its limited water resource to water provision, energy generation and agricultural production (the latter has a very high-water consumption factor of 62% due to irrigation ( Adom et al., 2022 ).

The reluctance to enforce integrative policies, driven by trade-offs across sectors in resource-limited countries like South Africa, poses significant challenges. As a water-scarce nation with ambitious plans for transitioning to renewable energy, the pressure on the water sector is pronounced ( Rasul and Sharma, 2016 ).

Global climate change, and climate variability exacerbates the challenges of WEF-nexus in South Africa. Increasing aridity has a direct knock-on effect on food security ( Schreiner and Baleta, 2015 ; Mabhaudhi et al., 2016 ), leading to hunger and a decline in the supply of nutritious food ( Wlokas, 2008 ). Extreme weather events such as floods and heat waves also cause health issues such as food and waterborne diseases and heat stroke ( Mabhaudhi et al., 2019 ) and exacerbates land degradation, especially of agricultural lands ( Wlokas, 2008 ).

Water and land are key natural resources that are already under pressure from competing interests. Climate change exacerbates these challenges, as it increases the demand for resources. In regions where land and water are limited, an upsurge in multi-service projects aiming to tackle food insecurity and promote clean energy could exacerbate competition for these vital resources.

The lack of dedicated funding to provide integrated solutions is another reason why the sectoral approach persists, as the implementation of the nexus requires significant investment. The current funding landscape in South Africa prioritizes individual WEF sectors, with cross-sectoral funding streams being scarce ( Mabhaudhi et al., 2018 ). This siloed approach creates several challenges among which includes:

• Competing priorities: Crises like the COVID-19 pandemic necessitate diverting limited resources to immediate needs like health and hunger alleviation ( Wlokas, 2008 ; Mabhaudhi et al., 2019 ). This can exacerbate other critical issues like energy insecurity and poverty, further hindering progress on the WEF-H nexus.

• Limited impact: Sector-specific funding often fails to account for the interconnected nature of the WEF-H nexus, hindering the development of holistic solutions that address multiple challenges simultaneously.

The implementation of the WEF-H nexus requires innovative technologies and robust data, yet South Africa faces significant limitations:

• Data scarcity and comparability: Data availability is limited, and existing data often suffers from inconsistencies in spatial scales and temporal trends, hindering effective analysis and planning.

• Technological lag: Access to and expertise in innovative technologies like smart agriculture and early warning systems is limited, impeding the development of solutions to address challenges like climate change and disease outbreaks.

• Amid unpredictable extreme weather events and the prevalence of diseases, there is also a lack of innovative technologies tailored to alleviate the resultant impacts imposed by these events. Even though they come at a hefty cost, technologies such as smart agriculture (to alleviate a 15% decline in agricultural yields by 2050 if global warming increased by 2°C ( Mabhaudhi et al., 2019 )), early warming or detection systems and cutting edge health facilities are a necessity for an integrated response. Another bottleneck in this is that these innovative and sophisticated technologies require, trained personnel to operate them, which is still a scarce skill in the country.

Lack of functional, effective, efficient, and equitable partnerships or collaborations to drive implementation is another barrier. The implementation of the WEF-H nexus requires partnerships as individual experts rarely have expertise across all its dimensions. All this comes with effective communication across all relevant stakeholders including communities, technicians and government officials to promote dialogue among partners towards balancing the decision-making process. At the moment there is ambiguity regarding the roles of communities and relevant stakeholders in the implementation of the nexus framework (D. Naidoo et al., 2021 ). Some of the stakeholders are also in need of capacity development and awareness which hinders collaboration and results in a lack of stakeholder involvement in the nexus framework ( Adom et al., 2022 ). For instance, about 73% of the participants in an interview study agreed that there are major gaps within stakeholder engagement in the nexus ( Adom et al., 2022 ).

The WEF-H nexus faces the challenge of navigating complex political and socio-cultural landscapes, where historical biases towards isolated sectors hinder balanced implementation. Achieving consensus across spheres and sectors requires addressing these challenges and fostering equitable development.

By design, the implementation of the WEF-H programme ideally requires a long period of time. It is possible that while implementing the WEF-H programme, the breadth and coverage of activities of WEF-H approach lend themselves to unintended delays that derail achievement of outcomes and impact. Pressured by the short terms in government, politicians and decision-makers may face pressure to show immediate results to meet political or economic agendas. This can lead to biased prioritization of short-term goals at the expense of the more comprehensive long-term goals of the nexus. Developing and revising policies to effectively enforce the WEF-H nexus demands meticulous consideration of numerous factors, inherently leading to a time-intensive process.

Getting the private sector to actively contribute to the implementation of the WEF-H nexus is another bottleneck. The focus of the private sector is profit. ‘What is in it for us’ has been the dominant and acceptable main focus of the private sector. The private sector is risk averse. Waiting for, encouraging, or coercing the government to absorb the inherent transactional risks has been one of the approaches that the private has used to minimize their exposure and ensure their profitability and sustainability. Despite these basic attributes of the private sector, it is evident that most sections of the private sector are looking for opportunities where they can make a positive societal impact. The WEF-H nexus provides such an opportunity. This leaves us with the question: Why has the private sector not seized the opportunities to implement the WEF-H nexus, especially in communities wherein they operate? Is it likely that there are actions inherent in the implementation of the WEF-H nexus that are laden with risks that the private sector is not willing to absorb?

7 Enablers for implementing the WEF-H nexus

Several ingredients for transitioning from “nexus thinking” to “nexus doing” are required for a successful implementation of the WEF-H nexus. This approach holds immense potential to provide lucrative opportunities for South Africa. This paper adapts the scaling framework and classify the nexus under a three-pronged scaling principles system consisting of (i) scaling up, (ii) scaling deep, and (iii) scaling out as illustrated in Figure 2 . Scaling up focusses on enabling factors that are policy and institutionally oriented, while scaling deep focus on culture and beliefs and scaling out centers on factors impacting greater numbers, the replication and dissemination of information on the WEF-H nexus. This results in an increased number of people or communities impacted. Lastly, scaling deep looks at enabling factors impacting on the cultural roots including aspects such as changing relationships, culture, and beliefs.

Figure 2 . Nexus enabling principles.

For this procedural and transformative transition to happen, several enabling factors have been identified in the literature which foster the adoption and implementation of the WEF-H nexus. The first factor identified is the investment in Capacity Development. To unlock the full potential of the WEF-H nexus, robust capacity development initiatives are required across stakeholders, encompassing government agencies, researchers, and local communities ( Chibarabada et al., 2022 ). These initiatives should encompass comprehensive training programs and knowledge-sharing platforms aimed at enhancing the understanding of nexus interlinkages. By equipping stakeholders with the necessary skills and insights, we empower them to make informed decisions that align with the holistic goals of the WEF-H nexus, thus catalyzing its effectiveness ( Ramos et al., 2022 ). Local communities can also benefit from educational programs on sustainable water and energy practices, alongside leadership development workshops to empower them to participate in decision-making processes.

Secondly, mobilization of finance is also an imperative factor when it comes to the WEF-H nexus implementation. Securing finances is pivotal to translating the WEF-H nexus from theory into impactful practice, regardless of the chosen institutional approach ( Hejnowicz et al., 2022 ). Southern Africa has witnessed a surge in research projects and publications concerning the nexus since 2013 ( Naidoo et al., 2021 ). For instance, the Southern African Development Community-European Union (SADC-EU) nexus dialogue-funded project has been instrumental in driving the WEF nexus from abstract research to tangible action across southern Africa. This initiative has led to the organization of numerous workshops, symposia, and science-policy dialogues within the region. Such financial commitments not only facilitate research and data generation but also provide the necessary resources for practical interventions and policy implementations that promote the sustainable integration of water, energy, food, and health systems.

Decision Support Systems and Frameworks are also a necessary ingredient. The development of robust decision support systems and frameworks is paramount in navigating the complex terrain of the WEF-H nexus ( Nhamo et al., 2020 ). These technological tools serve as indispensable guides for systematic analysis of intricate nexus linkages, enabling policymakers to scrutinize diverse scenarios and their potential ramifications on water, energy, food, and health systems. Decision support systems are the linchpin of informed and effective decision-making within the multifaceted landscape of the WEF-H nexus, fostering data-driven, evidence-based solutions that optimize resource allocation, minimize vulnerabilities, and bolster resilience across these interconnected sectors.

Innovative Policy Frameworks have also been identified as one of the enabling factors ( Naidoo et al., 2021 ). The dynamic nature of the WEF-H nexus necessitates adaptive and forward-thinking policy frameworks capable of accommodating its complexity. These policies should transcend sectoral boundaries, encouraging seamless integration and collaboration while emphasizing sustainability and resilience. The shared resources within the SADC region highlight the importance of harmonizing existing policies and linking them, as illustrated by the Revised Regional Indicative Strategic Development Plan. Such initiatives promote holistic resource management, acknowledge the interdependence of different sectors, and pave the way for comprehensive, cross-cutting policies that effectively address the WEF-H nexus’s challenges.

Regional Cooperation is also an important enabling factor that has been identified within the literature ( Decoppet et al., 2023 ) . Recognizing that environmental and resource challenges often transcend national borders, robust regional cooperation is essential. Collaborative efforts between South Africa and neighboring countries can effectively address shared WEF-H nexus issues, enhancing stability and mutual benefits while ensuring harmonized resource management. Given the overarching nature of environmental and resource challenges, regional cooperation may serve as a fundamental pillar in addressing the complexities of the WEF-H nexus. The SADC regional integration framework (Saurombe, 2010) could transcend beyond trade to include developmental trajectories that have a bearing on WEF-H nexus. South Africa’s geographical proximity to neighboring countries accentuates the necessity for collaborative endeavors. By forging strategic partnerships and alliances with neighboring nations, South Africa and other member states can collectively tackle shared WEF-H nexus challenges that transcend political borders. Such collaborative efforts foster stability, mutual benefit, and regional cohesion. Whether it is addressing transboundary water management, cross-border energy initiatives, harmonizing agricultural practices, or jointly responding to health crises, regional cooperation can yield synergistic solutions that are more effective and sustainable than isolated efforts within national boundaries. Additionally, regional cooperation can lead to enhanced resilience in the face of resource-related uncertainties and bolster collective capacity for responding to emerging WEF-H nexus issues.

Political will is another important enabling factor that fosters the adoption and implementation of the WEF-H nexus. A bedrock of strong political will is fundamental to prioritize the WEF-H nexus and commit to sustainable resource management and public health. Such commitment provides the foundation for integrated policies and action plans that genuinely address the nexus’s intricate challenges. A robust and unwavering political will stands as the cornerstone of meaningful progress within the WEF-H nexus. National leaders hold the key to prioritizing this integrated approach, committing to sustainable resource management, and safeguarding public health. Their dedication paves the way for the development and implementation of comprehensive policies and action plans that genuinely confront the intricate challenges posed by the nexus. It sends a resounding message that these issues are of paramount importance, transcending political cycles and short-term interests, and underscoring a commitment to the long-term wellbeing of both the environment and the populace.

Another necessary ingredient noted in the literature is the clear demarcation of WEF-H operational boundaries: Defining distinct operational boundaries for WEF-H initiatives is crucial as it ensures that roles, responsibilities, and accountabilities are well-understood, preventing overlaps or gaps in resource management, and fostering efficient and effective governance. This not only prevents wasteful overlaps and dangerous gaps in resource management but also fosters efficient and effective governance. By delineating the boundaries of action and influence, stakeholders can coordinate their efforts more effectively, resulting in streamlined operations and more impactful outcomes.

360-Degree stakeholder engagement that leaves no one behind is also another important enabling factor. This underscores the principle of inclusivity’s paramount importance is recognized. Engaging all stakeholders, including marginalized communities, is essential for equitable resource allocation and access ( Bruns et al., 2022 ; Hejnowicz et al., 2022 ). Such comprehensive engagement ensures that diverse perspectives and needs are considered. Engaging all stakeholders, without exception, is not only a moral imperative but also a strategic necessity. This comprehensive involvement ensures that the benefits and burdens of resource management are equitably distributed. Marginalized communities, often disproportionately affected by environmental and health challenges, must have their voices heard and their needs addressed. Inclusivity makes the WEF-H nexus genuinely holistic, drawing on a wealth of perspectives and insights to inform more equitable and effective policies and actions. To operationalize this approach, we propose several pathways for engaging all relevant stakeholders in the WEF-H nexus. Firstly, the establishment of inclusive platforms, such as community forums and online portals, can facilitate ongoing communication and collaboration. Secondly, targeted outreach and awareness campaigns can ensure that marginalized communities are actively involved. Thirdly, leveraging technology, such as mobile applications and social media, can enhance accessibility and engagement. Additionally, incorporating participatory approaches, like co-design sessions and citizen science initiatives, fosters a sense of ownership among stakeholders.

Unlocking the full potential of the WEF-H Nexus, demands breaking down siloed governance. Effective collaboration among government departments, private sector entities, civil society organizations, and academia creates a fertile ground for innovation which enables the sharing of knowledge, identify synergies, and address challenges holistically ( Lazaro et al., 2022 ). Imagine a fertile ecosystem where engineers, farmers, policymakers, and community leaders, all contribute to cross-pollination of ideas. This is the power of a multidisciplinary approach to the WEF-H nexus, where collaboration sparks innovation and ensures no facet is overlooked. From policy blueprints to grassroots implementation, every strand contributes to a more comprehensive and impactful solution, ultimately leading to more sustainable and equitable outcomes for food, water, energy, and health.

Establishment of open access databases and encouraging data sharing can also positively impact on the adoption and the implementation of the WEF-H nexus. Data transparency and sharing are cornerstones of the WEF-H nexus approach. Open access databases facilitate the exchange of information, supporting evidence-based decision-making and research that can drive sustainable resource management and public health improvements ( Mabhaudhi et al., 2021 ). Open access databases facilitate the seamless exchange of information among stakeholders, underpinning evidence-based decision-making, and research. With access to comprehensive and up-to-date data, policymakers and researchers can identify trends, track progress, and make informed choices that drive sustainable resource management and improvements in public health.

Innovative Technology is another enabling factor positively impacting on the adoption and implementation of the WEF-H nexus. Examples of these cutting-edge technologies include, but are not limited to, precision agriculture techniques that optimize water use, the integration of renewable energy sources to power nexus-related activities, and advanced health monitoring systems. Embracing cutting-edge technology within the WEF-H nexus enhances monitoring, data collection, and resource management. This includes the adoption of technologies that promote efficient water use, harness renewable energy sources, advance sustainable agriculture practices, and facilitate health monitoring, thereby driving innovation and progress across the nexus. Embracing cutting-edge technology is a catalyst for progress across the WEF-H nexus. By harnessing innovative solutions, stakeholders can drive meaningful change. Technology enhances monitoring, data collection, and resource management, leading to more efficient and sustainable practices that benefit both the environment and public health. It also fosters a culture of innovation, inspiring continuous progress within the nexus.

8 Conclusion

The exploration of water-energy-food-health (WEF-H) remains key in broadening our understanding of the nexus complexity. This article contributes to the body of knowledge which reveals a paradigm-shifting approach to addressing the intricate interdependencies among these critical sectors. Integration of the health dimension goes beyond conventional WEF frameworks, as it introduces a comprehensive understanding of human wellbeing and resilience. The study contribute to the ongoing discourse surrounding the WEF nexus demonstrating the advantages of linking the health sector. By synthesizing insights from various disciplines, our work advances the understanding of how health interplays with water, energy, and food dynamics. This contribution positions the WEF-H nexus as an innovative solution to complex global challenges. To realize its full potential, there is a need for dedicated champions who can not only navigate the enablers and barriers outlined in this study but also translate concepts into actionable plans and sustainable programs. The success of the WEF-H nexus requires collaborative efforts from governments, stakeholders, and communities, providing a unique and impactful framework for addressing the multifaceted challenges at the intersection of water, energy, food, and health. South Africa, like many nations, aspires to build capable governance, but the complexity of the WEF-H nexus approach may strain government resources. The nexus approach acknowledges the existence of various policies, plans, systems, and programs, but also recognizes that their impact can be amplified when integrated into a cohesive implementation framework from the outset. This should not discourage governments to invest resources in the nexus approach but highlights the inherent challenges in aligning governance structures with its holistic nature.

While the Water-Energy-Food-Health (WEF-H) nexus presents a promising solution to urgent global challenges, its successful implementation necessitates meticulous planning, dedicated champions, and strategic governance. Recognizing the need for a nuanced approach, our paper emphasizes the imperative of capacity development, cross-sectoral collaboration, and the formulation of integrated governance frameworks. These elements are not merely suggested but they could be integral components that address the complexities involved. By strategically integrating these aspects into the implementation process, we ensure that the WEF-H nexus may be closer to reaching its full potential without imposing undue burdens on existing systems. Throughout the paper, we have enhanced the discussion, providing earlier argumentation to articulate the critical role of capacity development and integrated governance, thereby reinforcing the foundation for our proposed strategies.

In conclusion the WEF-H nexus presents an extraordinary opportunity to break the mold of traditional development paradigms. Its unprecedented focus on interconnectedness allows us to address multifaceted challenges from water scarcity, energy and food security to health disparities in a truly comprehensive manner. This holistic approach promises not just incremental progress, but a paradigm shift towards sustainable and equitable development.

Author contributions

SSM: Conceptualization, Writing–original draft, Writing–review and editing, Funding acquisition, Investigation, Project administration. BKM: Writing–review and editing, Funding acquisition, Project administration, Supervision. SM: Writing–review and editing. MSM: Writing–review and editing. FVS: Writing–review and editing. TL: Writing–review and editing. SN: Writing–review and editing. TT: Writing–review and editing. JJ: Writing–review and editing.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The author(s) acknowledge that the financial support for the research, authorship and publication of this article was received from the Department of Science and Innovation (DSI) through a CSIR Parliamentary Grant (P1EGC02).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: WEF-H nexus, South Africa, enablers, barriers, policy alignment, sustainability

Citation: Mutanga SS, Mantlana BK, Mudavanhu S, Muthige MS, Skhosana FV, Lumsden T, Naidoo S, Thambiran T and John J (2024) Implementation of water energy food-health nexus in a climate constrained world: a review for South Africa. Front. Environ. Sci. 12:1307972. doi: 10.3389/fenvs.2024.1307972

Received: 06 October 2023; Accepted: 14 March 2024; Published: 25 March 2024.

Reviewed by:

Copyright © 2024 Mutanga, Mantlana, Mudavanhu, Muthige, Skhosana, Lumsden, Naidoo, Thambiran and John. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Shingirirai S. Mutanga, [email protected]

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Contamination of water resources by pathogenic bacteria

Pramod k pandey.

1 Department of Population Health and Reproduction, University of California, Davis, California, USA

Philip H Kass

Michelle l soupir.

2 Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa, USA

Sagor Biswas

Vijay p singh.

3 Department of Biological and Agricultural Engineering & Zachry Department of Civil Engineering, Texas A & M University, College Station, Texas, USA

Water-borne pathogen contamination in water resources and related diseases are a major water quality concern throughout the world. Increasing interest in controlling water-borne pathogens in water resources evidenced by a large number of recent publications clearly attests to the need for studies that synthesize knowledge from multiple fields covering comparative aspects of pathogen contamination, and unify them in a single place in order to present and address the problem as a whole. Providing a broader perceptive of pathogen contamination in freshwater (rivers, lakes, reservoirs, groundwater) and saline water (estuaries and coastal waters) resources, this review paper attempts to develop the first comprehensive single source of existing information on pathogen contamination in multiple types of water resources. In addition, a comprehensive discussion describes the challenges associated with using indicator organisms. Potential impacts of water resources development on pathogen contamination as well as challenges that lie ahead for addressing pathogen contamination are also discussed.

Introduction

Water-borne pathogen contamination in ambient water bodies and related diseases are a major water quality concern throughout the world. Pathogen contamination is a serious issue for almost all types of ambient water bodies, making its recognition and understanding essential (U.S. EPA [ 2012a ]). The United Nations identified improving water quality as one of the eight Millennium Development Goals (MDGs). Its target is to reduce the number of people without access to safe water by 50% by 2015 (WHO [ 2011 ]). Because of the overwhelming scientific evidence for climate change (IPCC [ 2007 ]), it is also important to understand how perturbations in weather patterns can potentially impact pathogen levels in water resources. To meet future demands of water for food, energy, and ecosystems, increasing water storage structures (i.e., dams) must be a component of long-range planning (World Bank [ 2010 ]). However, such new structures can potentially degrade water quality and exacerbate public health risk.

While several review papers are currently available (Bradford et al. [ 2013 ]; Pachepsky and Shelton [ 2011 ]; Pang [ 2009 ]; Jin and Flury [ 2002 ]; John and Rose [ 2005 ]; Jamieson et al. [ 2004 ]; Jamieson et al. [ 2002 ]; Arnone and Walling [ 2007 ]; Kay et al. [ 2007 ]), there is a manifest need for additional transdisciplinary studies that assimilate knowledge gained from multi-research endeavors studying pathogen contamination, and provide a comprehensive synopsis in order to comprehend the entirety of the problem. Therefore, the goal of this review is to present a broad research scope assessment of pathogen contamination of water resources and the associated challenges it presents. We synthesize the potential health risks imposed by pathogens in water resources by providing existing knowledge that covers surface water, groundwater, fresh water, and saline water. Further, the impact of water resources development on pathogen contamination, future challenges, and recommendations are summarized. In addition, we provide a brief discussion describing water-borne pathogen footprints and potential challenges associated with the use of indicator organisms for assessing water quality.

Health risk

Water-borne diseases (i.e., diarrhea, gastrointestinal illness) caused by various bacteria, viruses, and protozoa have been the causes of many outbreaks (Craun et al. [ 2006 ]). In developing countries, such as those in Africa, water-borne diseases infect millions (Fenwick [ 2006 ]). According to World Health Organization (WHO), each year 3.4 million people, mostly children, die from water-related diseases (WHO [ 2014 ]). According to United Nations Children’s Fund (UNICEF) assessment, 4000 children die each day as a result of contaminated water (UNICEF [ 2014 ]). WHO ([ 2010 ]) reports that over 2.6 billion people lack access to clean water, which is responsible for about 2.2 million deaths annually, of which 1.4 million are in children. Improving water quality can reduce the global disease burden by approximately 4% (WHO [ 2010 ]).

Although water-associated diseases in developing countries are prevalent, they are also a serious challenge in developed countries. A study by Arnone and Walling ([ 2007 ]), who compiled data of outbreaks in the U.S. (1986 – 2000), reported 5,905 cases and 95 outbreaks associated with recreational water. Gastrointestinal Illness (GI) caused by variety of different microbes and germs, which causes symptoms, such as diarrhea, nausea, vomiting, fever, abdominal pain, was responsible for about 29.53% cases. More than 27% of cases were caused by Shigella spp . In addition, 10.99%, 10.08%, and 6.59% of the cases were caused by Cryptosporidium parvum , Adenovirus 3, and Leptospira, respectively. Nearly 23% and 21% of the outbreaks were caused by GI and Shigella spp , respectively. In addition, 16.84%, 12.63%, and 7.37% of the outbreaks were caused by Naegleria fowleri , E. coli 0157:H7, and Schistosoma spp. , respectively. Besides acute gastroenteritis, major etiological agents such as Giarida , Cryptosporadium , E. coli 0157:H7, V. cholera , and Salmonella were the agents responsible for many outbreaks (Craun et al. [ 2006 ]). During the same period 437,082 cases and 48 outbreaks were caused by contaminated drinking water, of which about 95.89% of the cases were caused by Cryptosporidium parvum . Nearly 42% and 31% of the outbreaks were caused by Giardia lamblia and GI, respectively. Reporting statistics on water-borne outbreaks in the U.S., Craun et al. ([ 2006 ]) found that at least 1870 outbreaks (23 per year) occurred between 1920 and 2002. These reported outbreaks and their reported incidence of illnesses are likely to be an underestimation of actual numbers because of nonreported cases and missing exposure information. To protect public health, the U.S. EPA’s National Primary Drinking Water Regulations (NPDWRs) contain standards describing the Maximum Contaminant Level (MCL) – the highest level of a contaminate allowable in drinking water. The U.S. EPA has defined the MCL of various microorganisms, such as Cryptosporidium , Giardia lamblia , Legionella , and Total Coliforms (including fecal coliform and E. coli ), and viruses (U.S. EPA [ 2012b ]). The Maximum Contaminant Level Goal (MCLG) – the level of a contaminant in drinking water below which there is no known risk to public health, has also been proposed by the U.S. EPA. The MCLC levels for Cryptosporidium , Giardia lamblia , Legionella , and Total Coliforms are zero. The EPA requires 99% removal of Cryptosporidium in drinking water, and the removal percentages of Giardia lamblia and viruses are 99.9 and 99.99%, respectively. Although there is no limit for Legionella , EPA believes that if Giardia lamblia and viruses are removed/inactivated, then drinking water likely to be free of Legionella. The U.S. EPA requires routine sampling of drinking water for testing total coliform and E. coli , and if a routine sample is positive, then repeat samples are required. If, in any repeat sample, total coliform or E. coli is detected then the drinking water has an acute MCL violation. For a drinking water system that collects fewer than 40 routine samples per month, no more than one sample can be total coliform-positive per month. For a system that collects more than 40 routine samples, no more than 5% of samples total coliform-positive in a month is allowed (U.S. EPA [ 2012b ]).

Each year approximately 42,000 cases of salmonellosis are reported in the U.S. (CDC [ 2014 ]). Schistosomiasis is not reported in the U.S. because it is not endemic; however, 200 million people are infected worldwide. In 2011, about 1,060 cases of Guinea worm disease, caused by the parasite Dracunculus medinensis , were reported in many remote parts of Africa that do not have safe drinking water. Malaria, a protozoal disease of the Genus Plasmodium transmitted by mosquitos breeding in contaminated water, affects 300–500 million people, and causes over one million deaths each year (more than 90% of deaths in Africa). Overall the morbidity and mortality caused by contaminated water are enormous and need to be controlled by improving the security of safe water (i.e., recreational as well as drinking water) in both developing and developed countries.

Historical perspective of water-borne diseases

Water contamination has a long presence in human history, with descriptions in the Sushruta Samshita about water-borne diseases resembling cholera in an Indian text written in Sanskrit as early as 500–400 B.C. (Colwell [ 1996 ]). Although cholera infections have not been reported in recent years in developed countries mainly due to improved sanitation, millions of people each year continue to get infected by Vibrio cholera in developing countries (Nelson et al. [ 2009 ]). The World Health Organization reports about 3–5 million cholera cases and 10,000 – 120,000 deaths, mainly in developing countries, due to cholera every year. Over time, cholera has caused millions of deaths in developing as well as developed countries (Colwell [ 1996 ]; Okun [ 1996 ]). For instance, a major outbreak of cholera was reported in London in 1849. Dr. John Snow, a physician to Queen Victoria, showed a relationship between people infected by cholera and contaminated water (Snow [ 1854 ]; Colwell [ 1996 ]). Jordan et al. ([ 1904 ]), Ruediger ([ 1911 ]), Simons et al. ([ 1922 ]), and Rudolfs et al. ([ 1950 ]) provide excellent reviews on incidents during the early 19th century. Colwell ([ 1996 ]) reported that in the mid and late 18th century, cholera infected millions of people all over the world. The worst outbreak in recent memory occurred in Haiti following the devastating earthquake affecting the capital and surrounding regions, with almost a half a million cases, killing thousands of people (CDC [ 2011 ]).

Water-borne pathogen footprints and challenges

Indicator organisms are commonly used to assess the levels of pathogens in water resources; i.e., water-borne pathogen footprints of water resources. Monitoring the levels of indicator organisms (such as fecal coliforms, E. coli ) (Figure  1 ) is a common approach for quantifying the potential pathogen loads in ambient water bodies. For decades, public health officials/scientists have evaluated water quality by enumerating fecal coliforms and E. coli levels in rivers, lakes, estuaries, and coastal waters (Malakoff [ 2002 ]; Pandey et al. [ 2012a ]; Pandey et al. [ 2012b ]; Pandey and Soupir [ 2013 ]). There is, however, much debate regarding current indicator organisms and their ability to represent the potential presence of pathogenic bacteria. In addition, identifying the source of pathogens (e.g., human waste, animal waste, wildlife excreta, and waterfowl droppings) (Figure  2 ) is challenging (Malakoff [ 2002 ]; Dickerson et al. [ 2007 ]). There is potential to use a relatively new approach such as microbial source tracking (MST) to trace the origin of fecal coliform (Scott et al. [ 2002 ]; Grave et al. [ 2007 ]; Dickerson et al. [ 2007 ]; Ibekwe et al. [ 2011 ]; Ma et al. [ 2014 ]). In the past, the MST method was exploited by antibiotic resistance analysis to assess the impact of cattle on water quality on a watershed scale (Grave et al. [ 2007 ]). The authors suggested that host-origin libraries, based on a phenotypic method, are useful for tracking the pathogen sources. Many MST methods, however, rely on the assumption that some strains of bacteria are found only within a single kind or group of animals. This assumption can be debatable when it comes to the common fecal bacteria E. coli (Malakoff [ 2002 ]). Therefore, caution is needed while using E. coli for source tracking (Gordon [ 2001 ]). Further, the cost to develop libraries, implement extensive sampling programs needed for verifying the MST method, and calculate uncertainties associated with the method are legitimate issues, which requires attention before exploiting the MST method at watershed scale.

Transmission electron micrograph of E. coli (0157:H7; ATCC: 35150).

Challenges in identifying enteric pathogen sources (source: Malakoff, [ 2002 ] ).

Currently, public health officials/scientists rely on exposure limits for assessing pathogen levels in water resources, which have been established to protect human health. The EPA defines acceptable recreational limits as those that will result in eight or fewer swimming-related gastrointestinal (GI) illnesses out of every 1,000 swimmers (U.S. EPA [ 1986 ]). The current U.S. EPA fresh water quality criteria for E. coli is a geometric mean not exceeding 126 CFU/100 ml, or no samples exceeding a single sample maximum of 235 CFU/100 ml (U.S. EPA [ 2001 ]). Criteria were developed based on the U.S. EPA measurements of total and Highly Credible Gastrointestinal Illnesses (HCGI), which correlated with E. coli densities (r  =  0.804) in fresh recreational waters (Dufour [ 1984 ]). Multiple studies have identified trends between indicator organisms in water and GI illness in humans, including vomiting, diarrhea, and fever (Cabelli [ 1983 ]; Wade et al. [ 2006 ]). Recent work by Edge et al. ([ 2010 ]) detected water-borne E. coli in 80% of water samples with E. coli levels of less than 100 CFU/100 ml. Another study by Wade et al. ([ 2006 ]) reported significant positive trends between increased GI illness and indicator organisms at the Lake Michigan beach, and a positive trend with indicators such as E. coli at a Lake Erie beach. Recently, the use of indicator organisms (e.g., fecal coliforms, E. coli ) for assessing pathogen levels has been debated more often than ever; however, the use of indicator organisms is likely to continue for assessing pathogen levels in water resources potentially because of the lack of an alternative reliable solution.

Pathogen contamination in water resources

The U.S. EPA, which monitors water quality of various ambient water bodies, estimated that pathogens impair more than 480,000 km of rivers and shorelines and 2 million ha of lakes in the U.S. (U.S. Environmental Protection Agency [ 2010a ]). According to EPA estimates, pathogens are the leading cause of impairment for 303 (d) listed waters (i.e., list of impaired and threatened waters that the Clean Water Act requires all states to submit for EPA approval) (Figure  3 ) (U.S. EPA [ 2014a ], [ 2014b ], [ 2014c ]). A total of 71,917 causes of impairment have been reported, and the top five causes of impairment are shown in Figure  3 . Pathogen contamination clearly dominates the causes of impairment (U.S. EPA [ 2014a ], [ 2014b ], [ 2014c ]).

Causes of impairment in the U.S. (data source: U.S. EPA ( [ 2014a ] , [ 2014b ] , [ 2014c ] )).

Studies by Diffey ([ 1991 ]), Brookes et al. ([ 2004 ]), Jamieson et al. ([ 2004 ]), Gerba and Smith ([ 2005 ]), Gerba and McLeod ([ 1976 ]), Hipsey et al. ([ 2008 ]), Pachepsky and Shelton ([ 2011 ]) reviewed the current studies of water-borne pathogen transport, with particular reference to freshwater and estuarine sediments. In addition, many current reviews focus on specific aspects of water resources, for instance, John and Rose ([ 2005 ]) focused on groundwater, Brookes et al. ([ 2004 ]) focused on reservoirs and lakes, Jamieson et al. ([ 2004 ]) focused on agricultural watersheds, and Kay et al. ([ 2007 ]) reviewed catchment microbial dynamics. The review study presented here uses a relatively broader approach for understanding how water-borne pathogens can potentially impact public health and various ambient water bodies. In addition, existing challenges, while assessing pathogen levels in water resources are discussed.

Coastal and estuarine environments

In the U.S., elevated pathogen levels are a leading cause of impairments of coastal environments (U.S. EPA [ 2014a ], [ 2014b ], [ 2014c ]). Urban runoff and sewers have been identified as the primary source of coastal water impairments. Rippey ([ 1994 ]) reported about 400 outbreaks and 14,000 cases caused by pathogen contaminated coastal water since the late 1800s in the U.S. Impairments of coastal environments have major economic impacts on the U.S. For example, losses caused by pathogen contamination in Massachusetts are more than $75 million each year (Weiskel et al. [ 1996 ]). The studies, which elaborate various pathogens in coastal environment and their survival mechanism, are summarized in Table  1 .

Studies describing pathogen contamination in saline water (coastal and estuary environments)

The sources of coastal water contamination are: point discharges of treated and untreated sewage from shoreline outfalls, and non-point discharges. The non-point sources, such as runoff from naturally vegetated areas, discharge pathogens into coastal waters. Besides runoff from vegetated areas, the storm water runoff from urban, commercial, and industrial lands also discharges pathogens into coastal waters. In addition, other sources, such as malfunctioning or poorly sited septic systems, can also introduce significant amounts of pathogens (Sayler et al. [ 1975 ]; Howe et al. [ 2002 ]). Weiskel et al. ([ 1996 ]) reported that direct deposition of waterfowl feces was a considerable source of pathogens. Fayer and Trout ([ 2005 ]) summarized the transport of various pathogens, such as Giardia , Toxoplasma , and Cryptosporidium (zoonotic parasites) in the coastal environment. Moreover, the presence of sediment in seawater can also increase the survival chance of fecal coliforms, such as E. coli (Gerba nd McLeod [ 1976 ]; Goyal et al. [ 1977 ]). Solo-Gabriele et al. ([ 2000 ]) showed that the location and timing of storms of the coastal area in tropical and subtropical environments are also important factors that can potentially influence coastal water quality.

Previous studies have shown that the direct discharge of storm water runoff into coastal waters through storm drain systems can cause pathogen contamination, even where separate storm and sanitary sewer systems are in place. For instance, Weiskel et al. ([ 1996 ]) found that about 16% of the total fecal coliform inputs were caused by storm water entering Buttermilk Bay in Massachusetts. In addition, coastal rivers draining largely undeveloped watersheds with extensive riparian wetlands can be a natural source of fecal pathogens to coastal waters (Viau et al. [ 2011 ]; Staley et al. [ 2014 ]; Roberts et al. [ 2013 ]; Liang et al. [ 2013 ]; Wilkes et al. [ 2014 ]). On-site septic systems can also contribute significant amounts of fecal pathogens to coastal waters in low-lying fine-grained geological settings where saturated soils enhance pathogen growth. Weiskel et al. ([ 1996 ]) reported that shoreline wrack deposits could act as a reservoir of fecal bacteria, and the removal of wrack deposits from inter-tidal zones can improve the water quality of adjacent coastal waters.

Similar to the coastal environment, increasing water-borne pathogen levels in estuaries are a serious threat to public health. Human activities can impact estuary pathogen levels when they are adjacent to populated areas, and often provide a means of transportation and substantial recreation (Schriewer et al. [ 2010 ]; Pachepsky and Shelton [ 2011 ]). The most common pathogens, previously identified in estuaries by Rhodes and Kator ([ 1990 ]), were Vibrio cholerae , Giardia , Cryptosporidium , Salmonella , and Campylobacter spp. As shown in Table  1 , the presence of various pathogens (e.g., E. coli, C. perfringens, Clostridium, Salmonella ) has been reported in many previous studies. Municipal point sources are the primary cause of pathogen contamination in estuaries. Urban water disposed through combined sewer outflows is the cause of approximately 12% of estuary impairments in the U.S. (Arnone and Walling [ 2007 ]). Pathogens, including Vibrio vulnificus which carries the highest fatality rate of any food-borne pathogen in the U.S., were detected in the Gulf of Mexico Estuary (Lipp et al. [ 2001 ]; Baker-Austin et al. [ 2009 ]). Several studies discovered that bed sediment plays a vital role (i.e., with the release of particle-attached pathogens from bed sediment to a water column through a resuspension process) for the persistence and transport of pathogens in the estuaries (Smith et al. [ 1978 ]; Desmarais et al. [ 2002 ]). Previous studies have shown that pathogen growth and decay are influenced by environmental conditions. For instance, a study by Chandran and Hatha ([ 2005 ]) revealed that sunlight is a major factor that influences survival of pathogens like E. coli and S. typhimurium in the estuarine water.

Groundwater

Groundwater is heavily used all over the world as the primary source of domestic drinking water supplies, and contaminated groundwater certainly enhances risk to public health. Nationally, 40% of the U.S. domestic water supply originates from groundwater, and over 40 million people use groundwater as their drinking water via private wells (Alley et al. [ 1999 ]). Groundwater pathogen contamination has led to numerous disease outbreaks in the U.S.; for example, at least 46 outbreaks of disease occurred between 1992 and 1999, resulting in 2,739 cases of illness and several deaths (John and Rose [ 2005 ]). These are reported cases; due to underdiagnosis and underreporting, the actual morbidity is almost certainly higher.

Several studies have shown that microbial pathogens, such as Salmonella , E. coli , S. faecalis , and enteroviruses are relatively stable in groundwater (Bittion et al. 1983; Schijven and Hassanizadeh [ 2000 ]; Pang et al. [ 2004 ]) (Table  2 ). Controlling groundwater pathogen contamination has recently been emphasized in many countries, as pathogens can survive up to 400 days depending on the soil temperature (Nevecherya et al. [ 2005 ]; Filip and Demnerova [ 2009 ]). For example, identifying sources of groundwater pathogen contamination has received significant attention in France (Grisey et al. [ 2010 ]). Many studies reported that health risks caused by chlorine-resistant protozoans, such as Cryptosporidium spp. (Ferguson et al. [ 2003 ]; Kay et al. [ 2007 ]; Kay et al. [ 2008 ]), are considerable. One of the major concerns is that wetlands without lining might cause pathogen contamination of groundwater (Kay et al. [ 2007 ]). Similar concerns have been expressed in the United Kingdom by water regulators. The European Union (EU) has also emphasized protecting groundwater from pathogen contamination. Pathogen-contaminated groundwater can cause pollution in coastal environments. For example, a study of Buttermilk Bay has shown that groundwater is capable of transporting a large quantity of pathogens from surface to sub-surface water either by direct discharge or by discharge to rivers flowing into the bay (Moog [ 1987 ]; Weiskel et al. [ 1996 ]). The risk of contaminating groundwater particularly increases in areas where shallow aquifers exist. In these situations it is more likely that contaminated surface water or water from septic tanks can reach groundwater (Weiskel et al. [ 1996 ]). Precipitation events are likely to increase groundwater pathogen contamination because of contaminated ground water recharge.

Pathogen contamination in freshwater environment (ground water, rivers and lakes and reservoirs)

Pathogen contamination (e.g., bacteria, protozoa, and viruses) poses a serious risk in water resources. The transport of pathogens from surface water to groundwater increases the vulnerability of groundwater (Jin and Flury [ 2002 ]). These authors reported that 70% of the water-borne microbial illness outbreaks in the United States have been associated with ground water. Pathogens such as viruses are much smaller than bacteria and protozoa, and many can potentially reach groundwater through porous soil matrices. Jin and Flury ([ 2002 ]) reviewed the fate and transport of viruses in porous media to understand mechanisms and modeling of virus sorption, and concluded that factors such as solution chemistry, virus properties, soil properties, temperature, and association with solid particle influences virus survival, transport, and sorption in porous media. Pang ([ 2009 ]) studied microbial removal rates in subsurface media, and reported that soil types considerably influence microbial removal rates. For instance, volcanic soils, pumice sand, fine sand, and highly weathered aquifer rocks showed high removal rates. The author found that microbial removal rates were inversely correlated with infiltration rates and transport velocity.

Considerable work recently has been done towards understanding pathogen transport in the vadose zone (Wang et al. [ 2014a ]; [ 2014b ]; Unc and Goss [ 2004 ]; Darnault et al. [ 2004 ]). Groundwater can be contaminated by seepage and percolation of contaminated water from the vadose zone (Darnault et al. [ 2004 ]). The macropores of agricultural land are also known to play a considerable role in polluting groundwater, particularly from fields where manure is applied (Jamieson et al. [ 2002 ]). Unc and Goss ([ 2004 ]) evaluated the influence of manure on the transport of bacteria from land receiving manure to water resources. These authors reported that manure application in the land influences pathogen transport in the vadose zone. The presence of straw and coarse organic matter influences the persistence of bacteria, and manure application changes the physical configuration of soil, the soil chemistry, and the properties of the microbial cells, which control the survival and persistence of bacteria in soils. Another recent study by Wang et al. ([ 2014 ]) assessed the transport of E. coli in soils with preferential flow. The authors reported that a decrease in macropore length resulted in a decreased apparent saturated hydraulic conductivity of the macropore and an increase in the mass transfer. Wang et al. ([ 2014a ]; [ 2014b ]) concluded that macropore length has a considerable influence on preferential transport of E. coli .

Reservoirs and lakes

Previous studies have shown the presence of many pathogens in lakes and reservoirs (Table  2 ), and that these pathogens can pose risks to human health. In many countries surface reservoirs serve as the main source of drinking water, and these surface water bodies are often vulnerable to pathogen contamination (Kistemann et al. [ 2002 ]). In the developed world, although there is increased awareness of water treatment for pathogen contamination and water quality, outbreaks of water-borne disease via public water supplies continue to be reported (Gibson et al. [ 1998 ]; Howe et al. [ 2002 ]; Brookes et al. [ 2004 ]).

In the past, more than 403,000 residents of the greater Milwaukee, Wisconsin area experienced gastrointestinal illnesses due to infection with the parasite Cryptosporidium parvum following contamination of the city’s water supply, which was associated with inadequate filtration of contaminated water from Lake Michigan (Mac Kenzie et al. [ 1994 ]; Cicirello et al. [ 1997 ]). In the 1990s, Cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (Howe et al. [ 2002 ]). In developing countries, diseases such as diarrhea and cholera are the leading cause of morbidity (Nelson et al. [ 2009 ]). Overall, diarrhea associated with drinking contaminated water is responsible for 2 to 2.5 million deaths annually (Fenwick [ 2006 ]). In lakes and reservoirs, increased pathogens are often associated with storm events, and the stream inflow is considered to be the major source of pathogens during storm events. Elevated flows in rivers most likely agitate bed sediment, which causes enhancement of pathogen levels of the water column (Jamieson et al. [ 2005a ]; Jamieson et al. [ 2005b ]; Pandey and Soupir [ 2013 ]; Bai and Lung [ 2005 ]). During the rainy season, the influx of contaminated water from rivers to lakes and reservoirs can substantially increase pathogen levels (Kistemann et al. [ 2002 ]). The quantity of pathogen influxes from tributaries of lakes and reservoirs during the rainy season is of particular importance in determining pathogen transport and distribution (Brookes et al. [ 2004 ]).

Pathogen contamination is a major cause of stream impairments. The sources of impairment and health risks induced by water-borne pathogens are extensively reported (Table  2 ). In the U.S. pathogen contamination is the leading cause of stream water pollution. The EPA’s National Water Quality Inventory Report suggests that about 53% of the assessed rivers are impaired, and a majority of them are contaminated by pathogens (U.S. EPA [ 2012a ]). The cost to implement the total maximum daily load (TMDL) plans to improve stream water is estimated as $0.9 to $4.3 billion per year (U.S. EPA [ 2010b ]).

Pathogen influxes into rivers from agricultural lands (Figure  4 ) are the main cause of stream impairments (Chin [ 2010 ]; U.S. EPA [ 2012a ]). A weak understanding of pathogen transport from agricultural lands to rivers is considered to be a major challenge in implementing and deriving suitable land management practices capable of improving stream water quality. For instance, despite common knowledge that agricultural land’s non-point source pollution is a leading cause of stream impairment, it is difficult to identify points of origin of pathogens and the pathways by which they enter streams. As an example, pathogens are likely to enter rivers from many potential sources, including lateral inputs from pastures and riparian zones, influx of pathogen-contaminated groundwater, direct deposit of fecal matter from livestock and wildlife, discharge of contaminated sanitary sewer flows, and wastewater treatment plant effluents. In rainy events, pathogens in rivers are influenced by fresh input from watersheds as well as sub-surface flow. In addition, the resuspension of legacy pathogens from bed sediments can considerably increase pathogen levels (Cho et al. [ 2010 ]; Droppo et al. [ 2009 ]; Jamieson et al. [ 2005b ]; Kiefer et al. [ 2012 ]; Nagels et al. [ 2002 ]; Muirhead et al. [ 2004 ]; Kim et al. [ 2010 ]; Smith et al. [ 2008 ]).

Simplified path of animal waste pathogen transport from agricultural land to rivers.

Controlling pathogen contamination from livestock/wildlife to streams is challenging (Terzieva and McFeters [ 1991 ]). For example, it is doubtful that pathogen contamination can be prevented by fencing off riparian buffers, and even if buffers are useful in controlling stream water pathogens, it is not certain what their width must be (Nagels et al. [ 2002 ]). There are review studies that elaborate on stream water pathogen contamination (Fraser et al. [ 1998 ]; Jamieson et al. [ 2004 ]; Pachepsky et al. [ 2006 ]).

Many studies have emphasized the use of mathematical models to understand pathogen transport from agricultural land to rivers (Kim et al. [ 2010 ]; Muirhead et al. [ 2004 ]; Jamieson et al. [ 2005a ]; Jamieson et al. [ 2005b ]). Previous studies (Gerba and Smith [ 2005 ]; Pandey et al. [ 2012b ]; Pandey and Soupir [ 2013 ]; Pachepsky and Shelton [ 2011 ]; Martinez et al. [ 2014 ]) have emphasized the need to improve existing models for calculating the fate and transport of pathogens at the watershed scale. Currently, empirical as well as mechanistic models are being used to calculate microbial fate and transport (Muirhead and Monaghan [ 2012 ]). Numerous studies are available for exploiting watershed scale models such as WATFLOOD (Dorner et al. [ 2006 ]), the Soil and Water Assessment Tool (SWAT) (Neitsch et al. [ 2005 ]), the Spatially Explicit Deliver Model (SEDMOD) (Fraser [ 1999 ]), and KINEROS/STWIR (Guber et al. [ 2011 ]) for predicting pathogen transport. Though numerous watershed scale models are available, which can be exploited for calculating pathogen transport at watershed scale, considerable difficulties exist while using the models (Pandey et al. [ 2012b ]; Pandey and Soupir [ 2013 ]). For instance, correctly identifying the model input parameter values is a daunting task. Recently, considerable emphasis has been given to understand the sensitivity of the input parameters to the model output (Martinez et al. [ 2014 ]; Parajuli et al. [ 2009 ]).

When implementing watershed scale models for predicting pathogen transport, difficulties related to the selection of model input parameters are common (Martinez et al. [ 2014 ]). A study by Parajuli et al. ([ 2009 ]) evaluated the sensitivity of fecal coliform bacteria loads modeled with SWAT, and the authors reported that many of the parameters (e.g., bacterial die-off rates, the temperature adjustment factor) were insensitive to the model output. Similarly, Coffey et al. ([ 2010 ]) reported that initial concentration of E. coli and the bacterial partition coefficient parameters of the SWAT model were overly sensitive in affecting the model’s output. Another recent study by Martinez et al. ([ 2014 ]) evaluated the KINEROS/STWIF model input parameter sensitivities to the output. These authors reported that environmental controls such as soil saturation, rainfall duration, and rainfall intensity had the most sensitivity, while parameters such as soil and manure properties were the least sensitive in affecting model output. Many previous studies (Pandey and Soupir [ 2012a ], [ 2012b ]; Kim et al. [ 2010 ]; Martinez et al. [ 2014 ]; Parajuli et al. [ 2009 ]) reported that identification and selection of model input parameters are major challenges when implementing the model for predicting fate and transport of pathogens at the watershed scale.

Blooming of cyanobacteria

While water-borne pathogens are a serious concern, excessive algal bloom (Figure  5 ) in water resources can potentially limit their uses for recreation activities as well as for drinking water. Cyanobacteria (blue-green algae) have unique roles in oxygenation of the atmosphere (Hofer [ 2013 ]); however, their excessive growth or dense algal bloom in water resources diminishes the quality and quantity of light in the water column ([ U.S. EPA 2014b ]). When blooms are excessive, the risk of toxin contamination (released by harmful algal bloom (HABs)) is likely to be elevated. The HAB includes many types of algal taxa such as dinoflagellates, diatoms, and cyanobacteria. Eutrophication caused by excessive algal bloom can cause fish kills and reduce the diversity of aquatic life ([ U.S. EPA 2014b ]). In hypoxic water, dissolved oxygen levels can be less than 2 – 3 ppm (U.S. EPA [ 2014c ]). For example, in the hypoxic zone in the northern Gulf of Mexico, an area along the Louisiana-Texas coast, less than 2 ppm of dissolved oxygen concentration has been reported. This is believed to be caused by excess nutrients delivered from the Mississippi River, in combination with seasonal stratification of Gulf waters (U.S.G.S., [ 2014 ]). The largest U.S. hypoxic zone, which occurred in 2002 in the Gulf of Mexico, was about 13,518 square kilometers (U.S.G.S. [ 2012 ]).

Algal bloom in Squaw Creek, Iowa, U.S.

Freshwater cyanobacterial blooms produce highly potent cyanotoxins and cyanobacterial HABs, which can affect the liver, nervous system, and skin (U.S. EPA [ 2014b ]). Cyanobacterial blooms can be potentially detrimental to human and animal health, aquatic habitats, and aquaculture industries (Kaloudis et al. [ 2013 ]; Carmichael [ 2001 ]; Falconer [ 2005 ]; Codd et al. [ 1999 ]). Previous studies (Mackintosh et al. [ 1990 ]; Yoshizawa et al. [ 1990 ]) have shown that microcystins (i.e., cynotoxins) are hepatotoxic and act as tumor promoters through the inhibition of protein phosphatases, which play a key role in cellular regulation. Eutrophic water conditions combined with warm surface water temperatures (15 – 30°C) can potentially enhance cyanobacterial blooms in water (Oikonomou et al. [ 2012 ]; Vareli et al. [ 2009 ]). Currently more than 400 hypoxic zones exist in the world affecting 245,000 square kilometers (Diaz and Rosenberg [ 2008 ]). These dead zones in coastal waters have spread exponentially since the 1960s and have considerably impacted ecosystems. The increase in these dead zones is likely to be influenced by climate change. Various factors such as how climate change affects water-column stratification and how nutrient runoff affects organic matter production will determine further expansion of the dead zones (Diaz and Rosenberg [ 2008 ]). For instance, climate predictions of the Mississippi River basin indicate a 20% increase in river discharge, which will enhance nutrient loading and result in expansion of the oxygen depleted area (IPCC [ 2007 ]). Considering the importance of fresh water, estuarine, and marine environment to public health and aquatic life, identifying approaches capable of controlling excessive algal blooms is required before these dead zones spread globally.

Impact of water resources development

Water resources development involves altering the natural flow path of rivers and lakes, as well as designing irrigation schemes and dams. These activities have been alleged to be responsible for causing new diseases and enhancing health risks (Fenwick [ 2006 ]; Steinmann et al. [ 2006 ]).

The influence of water resources development in spreading diseases, such as schistosomiasis, a parasitic disease which is ranked second only to malaria with regard to the number of people infected, has been reported extensively; one estimate says that about 103 million out of 779 million infected people live in close proximity to large reservoirs and irrigation schemes (Steinmann et al. [ 2006 ]).

Designing dams and irrigation schemes in tropical and subtropical climate zones has often resulted in disease outbreaks caused by water-borne pathogens. Consider, for example, the Sennar Dam on the Blue Nile River and Sudan’s Gezira Scheme, the world’s largest irrigation project. Because of the dam’s commercial success, irrigation in the region has doubled from the 1940s and 1950s. After the 1950s, infections from malaria and schistosomiasis increased significantly, becoming the subject of the first integrated disease-control program, the Blue Nile Health Project, implemented from 1978 to 1990. The project failed to have any impact in controlling the prevalence of schistosomiasis (Eltoum et al. [ 1993 ]; Fenwick [ 2006 ]; Steinmann et al. [ 2006 ]). Another example is China’s Three Gorges Dam, built across the Yangtze River and completed in 2009, which created a 50,700 km 2 reservoir and submerged more than 220 counties. Hotez et al. ([ 1997 ]) reported that the reservoir would produce environmental changes that could lead to the transmission of schistosomiasis in the area served by the dam. A recent study by Schrader et al. ([ 2013 ]) found major high risk areas for schistosomiasis occurrence in the large lakes and flood plain regions of the Yangtze River. Another study by Gray et al. ([ 2012 ]) reported that the Three Gorges Dam will likely to impact the transmission of schistosomiasis in China.

In the U.S., because of increasing concern for produce safety, pathogen-free irrigation water is attracting considerable attention (Martinez et al. [ 2014 ]). Painter et al. ([ 2013 ]) reported that produce accounted for nearly half of food-borne illnesses in the U.S. between 1998 and 2008. Growing concern about the safety of food and water will likely help in developing improved strategies while planning and designing large dams for irrigation purposes.

Challenges and recommendations

Infectious diseases caused by pathogens are the third leading cause of death in the United States, and the leading cause in the world (Binder et al. [ 1999 ]). The past two decades have seen the emergence of many new pathogenic infectious diseases (Daszak et al. [ 2000 ]). Many of these are caused by anthropogenic changes, such as water resources development, climate warming, and interactions between humans and animals, both domestic and wild (Krause [ 1994 ]; Epstein [ 2001 ]; Woolhouse [ 2002 ]; Fenwick [ 2006 ]; Schriewer et al. [ 2010 ]).

Multidisciplinary knowledge about how ambient water bodies, wildlife, domestic animals, and human populations interact with and impact each other are crucial in dealing with future challenges. Generally, domestic animals, wildlife, and humans are considered to be major sources of water-borne pathogens; however, finding the specific culprit—the primary pathogen source—is challenging (Malakoff [ 2002 ]). A watershed, for example, can have many pathogen sources, such as agricultural land, riparian areas, agricultural feeding operations, livestock, wildlife, and humans.

Developing models that are reliable in predicting pathogen survival and transport at the watershed scale can be helpful in implementing/evaluating the strategies for mitigating ambient water body pathogen levels. Evaluating the impacts of various environmental factors on pathogen survival in water resources is crucial. Various publications (i.e., Dorner et al. [ 2006 ]; Kim et al. [ 2010 ]; Rehmann and Soupir [ 2009 ]; Droppo et al., [ 2011 ]; Cho et al. [ 2010 ]; Pandey et al. [ 2012b ]; Pandey and Soupir [ 2013 ]) are available describing models capable of predicting pathogen contamination levels in ambient water bodies; however, further work is required to improve model predictions. The evaluation of predictions by existing models clearly demonstrates the need for improvement. Many pathogen transport models use only temperature-induced mortality and growth, and do not include interactions among other environmental factors (e.g., pH, nutrients, DO, solar radiation); future inclusion of these environmental factors will likely to improve the model predictions.

Typically most studies have relied on E. coli and other indicator bacteria to indicate pathogen levels in water. Although widely used in monitoring contamination levels, E. coli alone can lead to mercurial and misleading information (Gordon [ 2001 ]). Schriewer et al. ([ 2010 ]) suggested that with improved pathogen detection technology (i.e., PCR-based detection) an indicator organism, such as E. coli , can be sufficiently accurate in most cases. Overall, improving technology to identify causative agents more accurately, creating standard epidemiological data for diseased populations, and enhancing the knowledge of disease dynamics can improve the understanding of risks caused by interactions among various populations (Harvell et al. [ 1999 ]; Daszak et al. [ 2000 ]; Harvell et al. [ 2002 ]).

In the past, a number of studies on pathogen contamination have been conducted on a scale where the conditions of ambient water bodies were simulated in laboratories. These studies are helpful in understanding pathogen behavior only up to a point. For enhancing the understanding of pathogen interactions in the environment, more emphasis should be given to field-scale studies.

Conclusions

This review examines studies from various disciplines to understand pathogen contamination in ambient water bodies. The worldwide prevalence of pathogen contamination is a serious concern, and enhancing the understanding of major pathogen sources and their significant impacts on water resources is crucial. A considerable number of studies on pathogen contamination have been conducted on a laboratory-scale; more emphasis should be given to field-scale studies for enhancing the understanding of pathogen interactions in the environment. Developing new models, and improving existing modeling approaches commonly used for predicting water-borne pathogen levels will likely to help in assessing pathogen contamination at watershed-scale. Considering the limited ability of existing models to predict pathogen contamination, improvement and development of new models are needed so that pathogen levels can be predicted more accurately. Integrating knowledge from multiple fields (e.g., hydrology, microbiology, and ecology) would increase the understanding of pollution levels and potential causes of pollution, and can also help devise long-term strategies to improve water quality.

Competing interest

The authors declare that they have no competing interests.

Acknowledgment

The authors thank the Division of Agriculture and Natural Resources and Veterinary Medicine Extension, University of California, Davis, and National Science Foundation (award No. CBET-0967845) for supporting this work.

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The Advent of Bodipy-based Chemosensors for Sensing Fluoride Ions: A Literature Review

• Published: 26 March 2024

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• Srabasti Chakraborty   ORCID: orcid.org/0009-0009-4171-3262 1  

The detection of fluoride ions in water and other sources is crucial because they can harm human health if they exceed the safe limit of 1-1.5 ppm. BODIPY (boron dipyrromethene) dyes are promising fluorophores for chemosensors, and their design and modification have attracted a lot of attention. Their advantages include visible light excitation and emission, high molar absorption coefficients (ε) and fluorescence quantum yields [ϕ (λ)], and flexible scaffold manipulation for various applications. In this article, we review the progress of BODIPY-based sensors for fluoride ions from the early 2000s to the present. We focus on the different scaffold modifications of the sensors and their corresponding responses, as well as the underlying photophysical mechanisms and potential uses of each sensor.

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The author is grateful to Dr. Tanusree Sengupta, Assistant Professor, Department of Chemistry, SSN College of Engineering, Kalavakkam, Tamilnadu, India for her help with academic resources. The author acknowledges the help extended by the authority of Behala College for carrying out the review work.

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Chakraborty, S. The Advent of Bodipy-based Chemosensors for Sensing Fluoride Ions: A Literature Review. J Fluoresc (2024). https://doi.org/10.1007/s10895-024-03619-7

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DOI : https://doi.org/10.1007/s10895-024-03619-7

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