Water, Sanitation, and Hygiene
Water, sanitation, and hygiene (WASH) is the area of environmental health concerned with the safe supply of drinking water, the safe management of human excreta and wastewater, and the hygiene practices that interrupt the transmission of disease between them. Because contaminated water and inadequate sanitation are among the leading environmental causes of preventable illness worldwide, WASH sits at the historical foundation of modern public health.
Definition
Water, sanitation, and hygiene (WASH) is the set of services and behaviours — safe drinking-water supply, safe disposal and treatment of human excreta and wastewater, and hygiene including handwashing — through which populations are protected from water-related and faecal-oral disease.
Scope
This area orients the reader to the public-health dimensions of water and sanitation: the determinants of drinking-water quality, the pathogens and chemicals that water can carry, the management of excreta and wastewater, and the contribution of inadequate services to the global burden of disease. It links to the detailed topics below and treats WASH as a reference and educational subject rather than as operational engineering or clinical guidance.
Sub-topics
Core questions
- How does the safety of drinking water, sanitation, and hygiene shape the population burden of disease?
- What pathways link inadequate water and sanitation to faecal-oral and other water-related infections?
- How is the disease burden attributable to unsafe WASH estimated, and how reliable are those estimates?
- What are the relative contributions of microbial versus chemical hazards in water?
Key concepts
- Faecal-oral transmission
- Drinking-water quality and safety
- Sanitation and excreta management
- Hygiene and handwashing
- Water-related disease (waterborne, water-washed, water-based)
- Attributable burden of disease
- Water safety planning
Mechanisms
WASH affects health chiefly by interrupting the faecal-oral pathway: human excreta containing enteric pathogens reach new hosts through contaminated drinking water, food, hands, and the environment, and safe water supply, sanitation, and hygiene each block one or more of these routes. Beyond infection, drinking water can also carry chemical hazards. The population effect of WASH is therefore typically expressed as the burden of disease attributable to inadequate services, estimated by combining exposure prevalence with relative risks from intervention studies (Prüss-Üstün et al., 2019; Wolf et al., 2014).
Clinical relevance
WASH is upstream of much of the infectious disease that clinicians encounter, particularly diarrhoeal illness, and understanding it helps interpret the environmental context of patient populations. This entry describes population-level determinants of health and the evidence linking services to disease; it is not a source of individual diagnostic or treatment advice.
Epidemiology
Inadequate water, sanitation, and hygiene remain a substantial cause of preventable disease and death globally, concentrated in low- and middle-income settings and falling heaviest on young children, largely through diarrhoeal disease (Prüss-Üstün et al., 2019; Wolf et al., 2014). Historically, the provision of clean water and sanitation in industrialising cities is associated with large declines in infectious mortality (Cutler & Miller, 2005), and meeting global water and sanitation targets has been estimated to require major sustained investment (Hutton & Bartram, 2008).
History
Concern with water and sanitation is foundational to public health: John Snow's nineteenth-century investigation of cholera in London linked the disease to a contaminated water supply, and the sanitary reforms and water filtration of the same era preceded large falls in urban infectious mortality (Cutler & Miller, 2005). In the twentieth and twenty-first centuries, WASH was formalised as a measurable determinant of the global burden of disease and embedded in international development targets (Hutton & Bartram, 2008; Prüss-Üstün et al., 2019).
Debates
- How large is the disease burden attributable to inadequate WASH, and how should it be estimated?
- Estimates of WASH-attributable disease depend on which exposures and outcomes are counted and on the relative risks drawn from intervention trials; methods have evolved over successive analyses, so headline burden figures should be read with their assumptions.
Key figures
- John Snow
- Annette Prüss-Üstün
- Jamie Bartram
- Sandy Cairncross
- Thomas Clasen
Related topics
Seminal works
- pruss-ustun-2019
- wolf-2014
- cutler-miller-2005
Frequently asked questions
- What does WASH stand for?
- WASH stands for water, sanitation, and hygiene — the safe supply of drinking water, the safe management of human excreta and wastewater, and hygiene practices such as handwashing.
- Why is WASH considered foundational to public health?
- Because contaminated water and inadequate sanitation drive much preventable infectious disease, and historical improvements in water and sanitation are associated with large reductions in infectious mortality.