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. 

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https://www.unep.org/interactives/wwqa/technical-highlights/health-and-water-quality