Health and water quality

Introduction

Water quality has been closely related to human health ¹ ever since John Snow linked a cholera outbreak in London to contaminated water in 1855.² Vibrio cholerae in water still plays a big role in the annual 1.4-4.3 million cholera cases that continue to occur globally. ³ The SARS-CoV-2 virus, which caused the COVID-19 pandemic, also enters the water cycle, as some COVID-19 patients shed the virus with their stool. ⁴ Although SARS-CoV-2 has been detected in wastewater, and in surface water receiving untreated wastewater, ⁵ so far there has been no evidence for presence of viable or infectious virus particles in wastewater, or for water as a transmission source. ⁶ Instead, the European Union launched a study, coordinated by its Joint Research Council and linked to the World Water Quality Alliance, to explore the potential of wastewater-based virus remnants as a sentinel monitoring concept.

But pathogens are not the only problem. Water is contaminated in a number of other ways that can threaten human health. The toxic compound arsenic is widely present in groundwater and can lead to skin, vascular and nervous system disorders, and cancer. ⁷ Recent estimates show that 94-220 million people are exposed to high arsenic concentrations in groundwater. ⁸ Similarly, fluoride, nitrate, heavy metals, and salinity in (ground)water pose human health risks.

Biotoxins formed by some cyanobacteria are a particular nuisance because bloom-forming species accumulate at the water surface, requiring closure of bathing sites and drinking water intakes. ⁹ As well, a large number of organic micropollutants coming from manufacturing and agriculture pose a health risk to the population. ¹⁰ These organic micropollutants can have a variety of impacts, such as disruption of endocrine, reproductive and immune systems. They can also cause cancer and diabetes as well as thyroid and behavioural problems . ¹¹ 

More recently recognized contaminants influencing human health include antimicrobial resistant microorganisms (AMR), microplastics ¹² or nanomaterials. AMR are a concern worldwide ¹³ because infections from them are often difficult to treat. Although the role of water in the spread of AMR is not yet quantified, its importance has been recognized. ¹⁴ 

The potential health risks from microplastics seem obvious, but knowledge of the extent to which they affect human health is limited. ¹⁵ And, though recent focus has largely been on the marine realm, UNEP will soon publish guidance on monitoring and addressing plastics in freshwater. ¹⁶ 

Water quality is related to human health through exposure. People are exposed to water in many different ways, depending on their location, livelihood, culture, wealth, gender etc. The most common exposure ways 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 exposure pathways highlight that the quality of ground, surface and coastal waters is relevant to human health.

In an earlier assessment, Snapshot of the World's Water Quality, ¹⁷ faecal coliforms were the contaminant included to represent human-health impacts. The assessment concluded that the rural population at risk of health problems, which is defined as those in contact with water contaminated with high concentrations of faecal coliforms, could be up to hundreds of millions of people in Latin America, Africa and Asia. ¹⁸ While this was an important realization, faecal coliform concentrations do not usually correlate very well with pathogen concentrations, as they can grow in the water body, ¹⁹ and many more contaminants can have human-health impacts. Therefore, this current assessment incorporates more water quality variables and exposure routes to assess the impact of water quality on human health.

Results

To evaluate the direct and indirect impacts of water quality on human health, we developed a non-exhaustive overview (see Table 3.1). This showed that there are a large number of direct and indirect links between water quality and human health, as well as interrelations between water quality variables, their sources, state, impacts and response. For example, pathogens and nitrate have to some extent the same sources and, therefore, potentially similar response options. But quantitative evidence for the links between water quality and human health are still largely lacking at continental or larger scales.

The global freshwater quality database GEMStat has data for a number of contaminants, but these data vary in space and time. For example, faecal coliform data are available for 6,451 stations across the world, while Escherichia coli data are available from 3,790 stations in North America, South America, Japan, and New Zealand. Data for Salmonella are available for 62 stations along rivers in Europe, but only for a few years in the early 1990s. For arsenic, many heavy metals, nutrients and organic micropollutants some data are available in GEMStat. Here we do not evaluate these data, because they are scattered and recent data for health are scarce. Instead, we report on potential data analyses that have been performed.

Table 3.1 The influence of water quality on human health. This list is non-exhaustive, as no detailed literature has been performed. The colour coding is blue for GEMStat or other large-scale databases; red for remote sensing; yellow for modelling; and green for a combination of GEMStat and modelling. Dark colours are for surface water, light colours for groundwater. 

^* The variable here is the state of the water quality variable for which data are available from GEMStat (https://gemstat.org) or other large-scale databases, or from remote sensing or models from the WWQA consortium for large spatial scales from continents to global.

^[1] Aw (2018); ^[2] Vermeulen et al. (2019); ^[3] Kiulia et al. (2015); ^[4] WHO (2015); ^[5] Codd et al. (1999); ^[6] Landrigan et al. (2018); ^[7] Schwarzenbach et al. (2010); ^[8] de Jesus Gaffney et al. (2015); ^[9] WHO (2012); ^[10] Ippolito et al. (2015); ^[11] aus der Beek et al. (2016); ^[12] Hughes (2002); ^[13] Internat. Progr. Chem. Safety (2002); ^[14] Amini et al. (2008); ^[15] Canter (1996); ^[16] Ouedraogoet al. (2016); ^[17] Strokal et al. (2016);^[18] Chowdhury et al. (2016); ^[19] Kumaret al. (2019); ^[20] Shammi et al. (2019); ^[21] van Vliet et al. (2020); ^[22] Vethaak and Leslie (2016); ^[23] van Wijnen et al. (2019); ^[24] Li et al. (2020).

Impacts

Human health and the change in it because of impaired water quality can be quantified through the mortality rate, which is one of the indicators of SDG 3 "Ensure healthy lives and promote well-being for all at all ages". For example, Indicator 3.9.2 is the "Mortality rate attributed to unsafe water, unsafe sanitation and lack of hygiene". ²⁰ The 2015 global burden of disease study attributed 1.8 million deaths to contaminated water from unsafe or untreated sources. ²¹ However, many diseases do not lead to death. Another common metric is the Disability Adjusted Life Year (DALY), which sums the years of life lost and the years of healthy life lost to quantify the disease burden. ²² DALYs can be added up across regions and diseases (see Figure 3.12). While DALYs are not yet commonly used as evidence for health impacts, another way of quantification is to estimate exposure, e.g. population in contact with contaminant. ²³ Additionally, the exceedance of safe water guidelines can be evaluated, such as the exceedance of drinking or bathing water guidelines.

But evaluations of health impacts because of impaired water quality are not yet widely available, and at large scale only for pathogens, arsenic and salinity. Models helped evaluate these health impacts. For Cryptosporidium, Quantitative Microbial Risk Assessment ²⁴ was used to evaluate the disease burden. Preliminary results for the population drinking surface water directly, and for the sub-Saharan population drinking surface water directly and tap water made from surface water, show that, in particular in Africa and Papua New Guinea, countries with a large share of people consuming surface water directly have the highest disease burden. The number of people in rural areas drinking surface water contaminated with faecal coliforms directly has decreased between 2008 and 2017, but at different rates across Latin America, Africa and Asia. ²⁵ To make the evaluation complete, this analysis should be repeated for other exposure pathways for other pathogens.

While the preliminary analyses for pathogens showed that Africa was a hotspot, Asia was the hotspot for arsenic in groundwater, both in terms of the most affected area as well as the proportion of the affected population. An estimated 94-220 million people are potentially consuming high arsenic concentrations in groundwater. This estimate of impact accounts for the proportion of households using untreated groundwater in both urban and non-urban areas of each continent.

For salinity, drinking water quality is classified as good when the concentration of total dissolved solids (TDS) is below 600mg/l. ²⁶ In many parts of the world strong reductions are required where surface water is used for drinking directly, in particular in northeast China, northern India, and countries east of the Caspian Sea. For heavy metals also these drinking water guidelines are frequently exceeded, and, across the world, surface water needs to be treated before consumption. ²⁷ 

 State

For many contaminants, no large-scale analyses of loads, concentrations, or other indicators are available from the literature. A complete assessment of all contaminants in all water types cannot yet be made, which implies that significant global health impacts remain unknown.

An overview of the contaminants for which the state is available at a large scale shows that hotspots are similar for many contaminants, including Cryptosporidium, faecal coliforms, ²⁸ insecticides, dissolved inorganic nitrogen (which includes nitrite and nitrate), salinity (TDS) concentrations and microplastics. These hotspots often closely link to the population density, the sanitation situation, and wastewater treatment efficiency in these areas, for example in China, India, Nigeria, the Middle East and some basins in Central and Latin America. For arsenic, the hotspots are slightly different, as these are closely linked to irrigation and/or geogenic background. Some areas overlap for these contaminants, such as in northeast China and Mongolia and in northwest India. The probability of having arsenic concentrations in groundwater larger than 10 mg/l is also particularly high along the Indus, Ganges and Brahmaputra rivers in South Asia and in north-eastern Argentina, while salinity has hotspots in the Middle East, North Africa and western parts of Argentina. For pathogens, concentrations vary throughout the year, but hotspots remain mostly the same.

The results in Figure 3.14 are mostly modelling results while Figure 3.15 demonstrates how remote sensing can be used as a proxy for exposure risk for potentially harmful phytoplankton blooms, including cyanobacteria. While mitigation of risk can already be effectively aided by remote sensing of larger surface waters (in the order of several km2), in-situ sampling will always be required to confirm the production of toxins at dangerous concentrations.

Sources

Main sources for most contaminants are anthropogenic emissions from domestic use, agriculture and manufacturing. In some cases, such as arsenic, fluoride, several heavy metals, nitrate and salinity in groundwater, geogenic sources can also play a role. For pathogens, point sources, which represent human faeces reaching rivers directly after open defecation or the use of hanging toilets, and indirectly through the sewer network and after treatment (if available), are often the dominant sources in urban areas. ²⁹ Diffuse sources, comprising livestock manure and faeces from people practising open defecation, are dominant in rural areas with sparse population. ³⁰ For dissolved inorganic nitrogen (including nitrate and nitrite) in surface waters, point sources, including sewers and untreated human waste from open defecation, are the main sources in northern Africa and South Korea. Direct discharges of animal manure from livestock production are a source in China, while in many other parts of the world diffuse anthropogenic sources, including the use of synthetic fertilizers and animal manure on land, atmospheric nitrogen (N) deposition on agricultural land, biological nitrogen (N₂) fixation by crops and from recycling of residues, are the main contributors. Main sources of salinity are irrigation return flows in Africa and Asia, manufacturing in Europe and North America ,and a combination of domestic waste and manufacturing in Latin America. ³¹ Finally, for plastics the main source of microplastics in rivers is mismanaged solid waste.

Response options

Reducing exposure to water of impaired quality will reduce health risks. Response options could include a reduction in the source emissions, treatment of the water before use or using a different water source, and prevention of the health problem, for example by vaccines or treatment. Other options include, among many others, improved water, sanitation and hygiene (WASH), manure management, reduced industrial emissions, and using drinking water filters or water from other sources.

The influence of response options can be evaluated using epidemiology studies in which the health effects before and after an intervention are evaluated. Additionally, scenarios can be used with the large-scale water quality and health impact models to evaluate the change in impact. One example at large scale evaluated the difference in pathogen emissions from humans to the surface water under different socio-economic development scenarios. The main conclusion was that improved wastewater treatment and eradication of open defecation are expected to reduce the human emissions to surface waters in the future, despite population growth. ³² Such scenario analyses have potential for evaluation of emissions to surface and groundwater, water quality and health risk for a range of contaminants. Finally, to increase the effectiveness of proposed response options, those managing water quality and public health need more collaboration and integration.

Data and knowledge gaps

There is still a strong need for better, more regularly monitored and up-to-date data to do a thorough evaluation.

Required research and action includes:

• Reporting on the state, impacts (also indirect impacts), main sources and response options for all contaminants causing health risks.
• Quantification of the impacts using DALYs, in order to sum up over the different contaminants.
• Evaluation of response options for multiple contaminants and using consistent and comprehensive scenarios, including consistent exposure estimates, throughout the assessment. These response options should maximize synergies and minimize trade-offs in reduction of multiple contaminants.
• Translation of response options to policy; institutional collaboration and integration across water and health disciplines is needed to implement responses effectively.
• More data on a wider range of contaminants and risks for validation as well as data-driven modelling. Only the salinity indicator for SDG 6.3.2 ³³ is directly related to human health and this chapter shows that many more indicators are important to consider in sampling schemes. In addition to country sampling schemes and despite its limitations, citizen science could also provide a relevant data source and create health impact awareness.
• Aggregation of the large number of project results at spatial scales smaller than continents. These publications will together be able to provide understanding of contamination levels and health impacts across the world.
• Improving the integration of all sources of information: in-situ data, models and remote sensing, across the DPSIR (drivers, pressures, state, impact, and response) table.

Adapted from World Water Quality Alliance (2021). World Water Quality Assessment:  
First Global Display of a Water Quality Baseline .