Key points

• Modelling has been a prominent approach to derive estimates on human health impacts from contaminated water, the water quality state, and the contamination sources. 
• First estimates of human-health impacts originating from the pathogen Cryptosporidium (single-cell parasite) shows hotspots in areas where surface water is still regularly used for direct drinking in Asia. This is true also for arsenic hotspots. For most other contaminants no impact studies are available at large scale.
• Concentration hotspots are, for most contaminants, densely populated areas where wastewater treatment is limited. For groundwater arsenic and surface-water salinity concentrations, hotspots include India, China and Mongolia.

Water, water everywhere, but is it good enough to drink?

Water quality has been linked to human health ever since a cholera outbreak in 1855 was attributed to contaminated water. Even today water is said to play a big role in the millions of cholera cases around the world each year. More recently, concerns were raised after the virus responsible for COVID-19 was found in wastewater at a number of locations. Though so far no evidence has been found for the presence of viable or infectious virus particles in these wastewater samples, the question of what viruses in wastewater can tell us has been included in a European Union monitoring study.

The toxic compound arsenic is widely present in groundwater and can lead to skin, vascular and nervous system disorders and cancer. Recent estimates show that 94-220 million people are exposed to high arsenic concentrations in groundwater. Similarly, fluoride, nitrate, heavy metals, and salinity pose human health risks.

Contact pathways

People are exposed to water in many different ways, depending on their location, livelihood, culture, wealth, and gender. The most common exposure pathways can be summarized as drinking, bathing, ingestion during domestic use, eating irrigated vegetables, rice (or rice products) or aquatic plants (such as water spinach), eating contaminated fish and shellfish, and skin contact. These pathways highlight that the quality of ground, surface and coastal waters is relevant to human health. 

An unknown burden

But evaluations of impaired water quality on human health are not yet widely available, and were only available at large scale for pathogens, arsenic and salinity. For Cryptosporidium, which can cause respiratory and gastrointestinal illness in humans, modelling was used to evaluate the disease burden. Preliminary results showed people drinking surface water directly have the highest disease burden. This was particularly true in Africa and Papua New Guinea, which have large share of their populations drinking surface water directly. Globally, rural populations directly drinking surface water contaminated with faecal coliforms decreased between 2008 and 2017, but at different rates across Latin America, Africa and Asia. Further analysis is needed to achieve a complete evaluation, including for other pathogens and other exposure pathways.

Key points

• In 2020, anthropogenic sources contribute more than 70 per cent to river nutrient loading.
• Most of the increase of river nutrient loading has been in Asia.
• Harmful algae blooms are now spreading in many river basins.
• Curbing global nutrient cycles requires paradigm shifts in food and waste systems.
• Two large-scale European assessments on ca. 2,000 chemicals report chronic effects of (a mixture of) chemicals on aquatic species to be expected at 42-85 percent of the studied sites, while 14-43 per cent of the sites are likely to experience some degree of species loss. 
• Assessments such as those done for Europe cannot be made on a global scale. Neither the measured data or the information to generate predicted concentrations are available yet. 
• The Human Impact and Water Availability Indicator (HIWAI) can be used to extrapolate results obtained for Europe. This proxy was found to correlate well with the expected loss of aquatic species in European surface waters. 

More people, more pollution

The world’s growing population, and the need to keep people fed and healthy, are contributing to two kinds of pollution that have a major impact on the health of the planet’s ecosystems: nutrient pollution and toxic stress by chemicals.

Nutrient pollution occurs when fertilizers, primarily nitrogen and phosphorus, used in food production or coming from untreated wastewater, enter soils, groundwater and surface water and are transported towards coastal seas. This can cause a number of problems, including groundwater pollution, loss of habitat and biodiversity, creation of coastal dead zones, harmful algal blooms, fish kills and human health impacts.

Harmful algae blooms may render water unsuitable for drinking, irrigation, bathing or swimming. Also, increased growth of algae may deplete oxygen, killing aquatic organisms. This may lead to bad odours that affect local tourism, and to massive fish kills that affect local fisheries. These algal blooms are becoming more and more common in world waters.
 

The importance of agriculture

In the Earth’s system, nutrient cycles have intensified dramatically in the past 50 years, with global nitrogen up 75 per cent and phosphorus up 92 per cent between 1970 and 2020. At the same time, the world’s population increased by three billion people. As a result, protein and phosphorus consumption and excretion also increased significantly, which reflects a growing number of people eating more meat and dairy products. However, nutrient flows related to food consumption are minor when compared to those from food production. Agriculture is now the most important source.

Aquatic life at risk

Around the world, about 40 per cent of the total population is connected to a sewage system, with wastewater treatment plants removing 26 per cent of the emissions from connected households. The remaining nitrogen and phosphorus in the untreated wastewater, plus effluents after treatment, contribute 15-17 per cent to total nutrient flows to water bodies.

Lake eutrophication, where nutrient pollution has caused an overgrowth of plants that depletes oxygen, poses a survival risk to aquatic organisms, affecting fisheries and aquaculture. Alarmingly, eutrophication is a worldwide phenomenon, with rapidly declining aquatic biodiversity.
 

A heavy load

Toxic stress from chemicals is when some of the more than 350,000 chemicals registered for use, or combinations of them, accumulate in rivers, lakes and seas, damaging aquatic life. Typically, these chemicals are used in agriculture, for food production, or in pharmaceutical products to keep us in good health.

In general, increasing economic development leads to an increasing use of a wide range of chemicals. 

Global chemical sales (excluding pharmaceuticals) are projected to grow from €3.47 trillion in 2017 to €6.6 trillion by 2030, with Asia expected to account for almost 70 percent of sales by then.

Key points

• First estimates of water-quality impacts on food security show hotspots in north-eastern China, India, the Middle East, parts of South America, Africa, Mexico, the United States and the Mediterranean. 
• Estimates reveal that more than 200,000 km² of agricultural land in South Asia may be irrigated with saline water exceeding the Food and Agriculture Organization guideline of 450 mg/l, and more than 154,000 km² show a high probability of groundwater arsenic concentrations that exceed the World Health Organization guideline of 10 µg/l.
• Aquaculture and mariculture (marine farming) production are important to produce high-quality protein, but both can be at risk because of water pollution, such as increased nutrient concentrations.
• Wastewater reuse in irrigation is an option to overcome water shortages and to close the nutrient cycle, but the food produced may become contaminated by pathogens (and faecal coliform bacteria), antimicrobial resistant microorganisms, and chemicals if wastewater has not been treated sufficiently.

We are more and more dependent on irrigation for the food we eat, but the impact of water quality on food products and industries is often underestimated.

Population growth, increasing incomes and dietary changes have meant a need for greater food production, and, globally, an estimated two billion people do not have regular access to safe and sufficient food. Water plays a central role in food production, as crop yields are higher from irrigated land. Some 40 per cent of crop production worldwide is harvested from irrigated land, which can be cultivated more than once a year under favourable water and climate conditions. Globally, about 70 per cent of abstracted water is used in agriculture.

Risk factors

One of the biggest risks from irrigation is an increase in salt in the soil, which can reduce crop yields. About 34 million hectares, or 11 per cent of global irrigated land, are affected by salinization, 77 per cent of which is in Asia, particularly in Pakistan, China and India.

Another risk is arsenic, which can accumulate in topsoil. It also bioaccumulates in vegetables, rice and other crops, which poses a risk for food-chain contamination and human health. Arsenic is present in trace amounts throughout the Earth’s crust and may leach into groundwater. If that groundwater is then used for irrigation, food safety may be compromised. In South Asia, more than 154,000 km² of agricultural land may be irrigated with water that exceeds the World Health Organization guideline for arsenic.

Fish and shellfish produced by aquaculture in cages both contribute to water-quality deterioration and are at risk from it. Nutrient pollution – nitrogen and phosphorus run-off from fertiliser use or untreated wastewater – can contribute to harmful algal blooms in aquaculture ponds.

Other pollutants, including microplastics and Triclosan, an antibacterial and antifungal chemical used in hygiene products, flow to rivers and seas from sewage systems and poorly handled solid waste.  These could enter the food chain and have an impact on human health. River basins with high Triclosan and microplastics inputs are mainly located in Europe, India, China and some individual sub-basins in South and North America.

What it all means

Food safety is affected by the quality of water used in irrigation, and also by that along the entire supply chain from food production to consumption. Water used in each step of the supply chain can be a source of exposure to various contaminants, such as pathogens, heavy metals, persistent organic pollutants, Triclosan and microplastics.

Food security and safety cannot be achieved without tackling water issues, since lack of safe water worsens food insecurity. Polluted irrigation water damages health and nutrition and reduces food production, constraining agricultural and economic development, especially in densely populated regions where water is already scarce and wastewater treatment is poor.

It is difficult to quantify the impact of water quality on food security because the necessary data are often lacking. Data derived from water-quality modelling in combination with remote sensing can close data gaps, identify hotspots, and map pollutant intakes.

Key messages

•  The increasing availability of free-to-access satellite data can radically transform how we assess and monitor inland waters.    
• Space agencies and stakeholders must work together to co-develop the next generation of ‘better, cheaper and faster’ satellite-based water services.

Why inland waters?

Inland water bodies, such as lakes, reservoirs and rivers, are extremely important to human societies. These waters play a crucial role in human health and well-being, supplying water for drinking (humans and animals) and food (irrigation, fisheries and aquaculture). They create vital ecosystems, supporting high levels of biodiversity and contributing to the global carbon and nutrient cycles. Moreover, lakes and reservoirs store information from the entire basin and so act as records of environmental change.

Despite their importance, many inland water bodies are under severe pressure, including from pollution, invasive species, extraction of upstream water, and climate change. As they connect three-quarters of the Earth’s terrestrial surface with the oceans, the study of inland waters is key to monitor the impact of such pressures. 

Water quality and lakes

Lakes come in many shapes and sizes, from small urban ponds, through constructed reservoirs, to the largest transboundary lakes. Collectively, these ecosystems are critical in supporting many societal needs. These include the provision of food and clean water, navigation, achieving Net Zero Carbon climate ambitions and renewable energy production, reversing biodiversity loss, delivering national and international food and non-food trade objectives, supporting livelihoods and creating jobs. 

The current environmental status of lakes is one of large-scale degradation, threatening their societal and economic value and incurring significant loss and damage. One of the main pressures globally is nutrient pollution from agriculture and wastewater, although effects of climate change, plastic pollution, hydrological alteration, industrial waste discharges, invasive species infestations, and habitat destruction are also prevalent.

‘Undervalued, understudied, and overlooked’

The current global approach to lake management is inadequate. Local to global management responses remain fragmented, under-resourced and undervalued. If left unchecked, societal impacts are predicted to substantially worsen in the coming decades. Global analyses project that by 2050 these impacts will include a decrease in the value of ecosystem services (currently estimated at $US3 trillion) by up to 20 per cent; a doubling (at least) of nutrient pollution from agriculture and wastewater, costing hundreds of billions of dollars a year to address; increased methane emissions from lakes with global societal costs estimated in the trillions of dollars; and a further increase in the rate of biodiversity loss from freshwater ecosystems, which is already higher than in any other biome. 

Lakes and reservoir ecosystems are undervalued, understudied, and often overlooked. Yet, they are of crucial importance for food security, the provision of clean water for drinking and irrigation, energy production, navigation, recreation and biodiversity. The global value of freshwater ecosystem services is in the order of trillions of dollars.1 The importance of exposure to nature in managing mental health and improving well-being is also becoming increasingly apparent. For example, access to ‘blue-green spaces’, including lakes, reduced mental health impacts of severe lockdown during the COVID-19 pandemic.2 

1 Costanza et al, (2014). 

2 Pouso et al, (2021). 

Key points

• Cape Town’s groundwater is vulnerable to water-quality impacts from urban development in an area with various land-use activities, posing a risk to the planned potable water supply. As a results, aquifer protection zones were co-designed. 
• Key water-quality challenges at Lake Victoria were identified as eutrophication; algal blooms (including cyanobacteria); hypoxia, and siltation/turbidity affecting fish breeding. Water quality data and information products and services being co-developed are a coastal eutrophication assessment, water temperature and stratification dynamics, and sediment chemistry.  
• The Volta Basin water-quality impacts were identified as domestic and industrial effluent, mining impacts, agricultural runoff, and aquaculture; expected to be exacerbated in the future by climate change, population increase, urbanization, and land-use change. Water quality product options being explored are a tool to determine the percentage of populations vulnerable to poor water quality, and a remote sensing-based groundwater quality assessment.

Water-quality Africa Use Cases

Three locations in Africa were selected for Use Case studies focused on urban groundwater (Cape Town), a lake of ecological and economic importance (Lake Victoria and associated basin), and a watercourse with pathogen risks (Volta River). The goal was to identify priority water-quality issues and hotspots and to co-design, pilot and demonstrate innovative information services and their application for water-quality improvement with the potential for upscaling and operational use. In the mid- to long-term, the World Water Quality Alliance hopes to build on experience here to provide further services to improve water quality, engage with UN Country Teams, and enable upscaling to other locations. 

Cape Town

The Atlantis, Cape Flats and Table Mountain Group aquifers were all targeted by the City of Cape Town as a potential potable water supply. The Cape Flats and Atlantis aquifers were vulnerable to pollution from urban settlements, resulting in salinization and anthropogenic contamination with nutrients, microbiological and industrial contaminants, hydrocarbons and other contaminants. The Table Mountain Group aquifer, on the other hand, was in relatively pristine areas with good water quality, but had naturally occurring elevated concentrations of iron and manganese. 

Extensive monitoring data was collected and presented to a meeting of stakeholders, and, as a result, the City of Cape Town and agricultural users of the aquifer suggested that a plan be co- developed to protect water quality. The scheme sets up groundwater protection zones around abstraction boreholes, identifies and maps contamination activities, and restricts them where the risk is high.

Lake Victoria Basin

Africa’s largest lake, Lake Victoria, is split between three countries, Kenya, Uganda and Tanzania. Working with stakeholders from the three countries, the central aims of the Use Case were to collectively assess water-quality challenges and associated impacts at Lake Victoria and its catchment, develop a stakeholder network, and assess data sources and types associated with the lake, and any limitations to the sharing of such data.

Key challenges identified included eutrophication, algal blooms, hypoxia and turbidity. Water quality data and information products and services being co-developed are a coastal eutrophication assessment, water temperature and stratification dynamics, and sediment chemistry. 

Volta Basin

A Stakeholder Engagement Workshop was held in Accra, Ghana, to assess the water-quality hotspots and to initiate a bottom-up social engagement process. 

The key challenges identified were poor sanitation resulting in elevated bacterial contamination, mining activities, industrial effluent (including plastics and microplastics), agricultural runoff of fertilizers and pesticides, and water-quality impacts to and from aquaculture. A further challenge is there is not a consolidated national government department mandated to do water quality monitoring, with this role currently split.

Discussions about potential in-country partnerships and water-quality product and services are continuing, but these may include a tool that translates poor water quality into estimates of impacts on affected populations, and a mapping and assessment of groundwater quality. 

Key points

• Water quality data gaps are evident globally but are most pronounced in low-income countries.
• Regardless of the data availability, assessment procedures are often unsuitable for the protection or restoration of water bodies.
• Strengthening national organisations to monitor and assess water quality has multiple benefits.

Differentiating between natural and water quality changes caused by humans is essential to understanding complex freshwater ecosystems. Individual countries must be responsible for monitoring their water but to do that they must have access to the systems and processes that enable one to collect and manage data in order to efficiently assess the situation whilst applying logical and rigorous water-quality criteria. This conversion of data into knowledge will only be of use if the conclusions of such a process are well-disseminated and result in the implementation of effective solutions. This procedure is absent or inadequate in many countries and this is so, more often than not, in countries which desperately need solutions and sound decision making.

Freshwater around the globe is under extreme pressure due to numerous reasons. The onset of climate change has added yet another direct threat and another layer of uncertainty as to how these freshwater systems will confront the challenges of the future. This uncertainty is something that society cannot afford. For example, it is essential to know whether a lake will be able to support the current fishery or drinking water supply in five, ten- or twenty-years' time. Otherwise, one is not able to take effective remedial action. An active relationship between a supporting organisation and the country in question can provide useful information, but a global overview that permits society to appreciate the situation as a whole, whilst comparing the results of individual states has so far been unavailable. Climate change, pollution, habitat destruction and fragmentation, the extraction of too much groundwater and land use practices that are detrimental to freshwater ecosystem health mean that we are, at present, in uncharted territory.

Many of the countries that lack the capacity to monitor and assess their freshwater systems are in regions where climate change impacts are predicted to be felt most severely. Although a large number of countries do collect data, the quality of their freshwater systems still continue to deteriorate. The reasons for this degradation are often related to non-scientific issues such as inappropriate legislation or a lack of enforcement of existing regulations. However, much would still be gained if the information that is generated by the collection of data were properly assessed and transformed into the basis of realistic, effective action.

An assessment is effective if one knows how to understand the factors that have resulted in current water quality trends. This can be achieved by applying criteria based on the use of the water such as knowing the quality of water which is required for drinking or irrigation or factors that consider the health of the ecosystem in order to maintain natural or near-natural conditions. For the latter, the creation of a baseline is essential. If the state of the water quality in an ecosystem changes, the existence of a baseline allows one to identify such a deviation quickly and therefore take action to restore the situation far more effectively. The maintenance of freshwater systems permits society to preserve ecosystems and benefit human health, to ensure opportunities for employment and to guarantee the production of food. In order to achieve this, long-term water quality datasets and a robust assessment capacity are necessary. The capacity to identify gaps and establish where the capacity of individual countries requires support and strengthening represents an important first step in this process. Objective and reliable science-based information is needed to increase the capacity to resist climate change, especially in those countries at present, most at risk.

Anthropogenic contaminants are a growing concern. So far, more than 350,000 chemicals and mixtures of them have been registered for production and use, and numbers are increasing. As a result of their use, many of these chemicals find their way into freshwater systems and coastal waters.

The EU-project SOLUTIONS 1 has developed a method to determine to what extent the full range of man-made chemicals is likely to negatively affect the ecological status of surface water. As an indicator for the predicted environmental concentrations of these chemicals, a measurement known as the multi-substance potentially affected fraction of species (msPAF) is used, which ranges from 0 (no species affected) to 1 (all species affected). This indicator can be linked to the Sustainable Development Goal Indicator 6.3.2 "Proportion of bodies of water with good ambient water quality". Values below 0.05 (meaning less than five per cent of species are expected to be potentially affected) represent a low risk and can be seen as a good ambient water quality (shown on the maps below as green areas).

As part of the United Nations World Water Quality Assessment, and with co-funding from the United Nations Environment Programme, this method has been applied at a global scale, combining a high-resolution (1 km x 1 km) hydrological model (Wflow SBM: https://github.com/Deltares/Wflow.jl) with the modules on emissions (D-Emissions) and water quality (D-WaterQuality). The models are setup using the open-source package hydromt ( https://deltares.github.io/hydromt/latest/), which is developed under the umbrella of the BlueEarth Digital Environment ( https://blueearth.deltares.org/).

Calculating quality

A Baseline calculation for 2010 and two different scenarios for 2050 have been simulated for future projections. The socio-economic pathway SSP2 (a middle of the road pathway or business-as-usual world) is combined with the RCP6.0 scenario and a more extreme combination of SSP5 (high growth of income, fossil fuel-based) in combination with high global average radiative forcing values of the RCP8.5 scenario.

In the Baseline situation in 2010 on a global scale 91 per cent of water bodies show a "good quality" (msPAF < 0.05), although large differences can be seen between the various global regions: the lowest percentage of water bodies with "good quality" are shown in the highly industrialized areas of Asia (76 per cent), Europe (83 per cent) and North America (84 per cent).

Key messages:

• Despite ongoing research, there is great uncertainty about the amount of plastic in the environment
• Plastics accumulate in terrestrial and aquatic environments, making them a long-term source to freshwater and the oceans even if the mismanagement of waste is stopped.
• Small urban rivers can contribute substantially to plastic export to the oceans
• Local actions to reduce inputs to rivers in urban coastal areas can effectively reduce plastic export to the oceans.
• Monitoring plastics in rivers, even by simple means such as counting floating objects, helps to shed further light on plastic transport in rivers and to confirm, for example, the success of measures to reduce plastic pollution in river

Plastics everywhere

Plastics as a product are a success story. Production of plastics has grown faster than GDP (Geyer et al. 2017). The properties of plastic that make it so successful, its durability, light weight and low cost production, are also the cause of its mismanagement and leakage. For example, about 40% of its production are single use items.

Since the presence of plastics in the oceans was first identified in the 1970s (Carpenter et al. 1972), plastics in the environment are now considered a global environmental problem. A growing number of studies have shown that plastics are found almost everywhere (Morales-Casalles et al. 2021). Their widespread occurrence and the fact that pollution of soils, lakes, rivers, and oceans is irreversible make plastic pollution a global environmental threat (MacLeod et al. 2021). Consequently, plastic production, waste generation and its fate in the environment are addressed by the Sustainable Development Goals (SDGs) established by the United Nations dealing with Sustainable Cities and Communities (SDG 11), Responsible Consumption and Production (SDG 12) and Life Below Water (SDG 14).

Furthermore, SDG 6 (Clean Water and Sanitation) has an indirect relation to plastics, as plastic garbage may block waterways and cause hygienic problems and plastics-associated chemicals can enter drinking water resources.

Understanding groundwater quality

Groundwater provides about half of the world's drinking water and more than 40 per cent of agricultural water. It is a key freshwater resource for meeting the Sustainable Development Goals, 1 yet is not always included in water quality assessments.

Agriculture, urbanization, industry, population growth, and climate change all are threats to groundwater quality, as is the use of fertilizers, herbicides, fungicides and other pesticides.

Domestic wastewater systems are a source of numerous organic contaminants, as well as bacteria, viruses and macronutrients. 2 This is especially so where wastewater systems such as pit latrines and septic tanks are used near supply wells that access shallow groundwater. 3

Poor siting, operation and maintenance of groundwater supply infrastructure cause significant threats to groundwater quality and in severe cases render groundwater supplies unfit for consumption. 4 Pumping-induced salinity is a major threat to groundwater, particularly in coastal areas and more arid terrains, or in regions where groundwater levels are particularly shallow (e.g. due to wetlands, discharge zones) as well as areas of irrigation. 5

Climate change

Climate change also poses numerous threats to groundwater quality. 6 These include sea-level rise, more intense storm surges affecting coastal aquifers, as well as more intense precipitation and flooding leading to greater ingress of surface contaminants and damage to groundwater infrastructure. Land use changes linked to changing climate are also a potential threat to groundwater quality as are changes in global temperatures, e.g. changing survival times for groundwater microbes and physical and biochemical reactions linked to carbon breakdown. 7

Natural contaminants

Two widely documented geogenic contaminants are arsenic and fluoride, although others include iron, manganese, chromium and radionuclides such as uranium, radium and radon. At high concentrations these can lead to serious health problems such as cancers in the case of arsenic, or dental and skeletal problems in the case of fluoride. Elevated iron and manganese concentrations commonly cause aesthetic - metallic taste and staining of cloth - and operational issues such as clogging of boreholes, pumps and water reticulation infrastructure, and can be a critical factor in the success of groundwater supply systems. Naturally occurring high salinity may also compromise groundwater quality and restrict use for drinking water and irrigation.

Assessing quality

A global groundwater quality portal 8 is being developed. Its aim is to be the focal point for global groundwater quality information and activities, to improve the global knowledge base, and to link to other portals and activities at regional to global scales.

A global groundwater quality assessment is needed because human activities and climate variability are increasing the pressure on groundwater resources.

Adapted from Misstear, B., Vargas, C.R., Lapworth, D. et al. A global perspective on assessing groundwater quality. Hydrogeol J 31, 11-14 (2023). https://doi.org/10.1007/s10040-022-02461-0 

1 IAH (2017).

2 Lapworth et al. (2017).

3 Graham and Polizzotto (2013).

4 Misstear et al. (2017).

5 Foster et al. (2018).

6 Barbieri et al. (2021).

7 McDonough et al. (2020).

8 IGRAC (2021).

A number of tools to aid in assessing water quality is available. Some of them are featured here.

Assessing world water quality brings together a range of scientific disciplines and methodologies, as well as consideration of human-influenced factors such as urbanization, pollution and climate change. Reflections on some of those issues appear here.