WASH mainly refers to: 

• Water: Supplies for drinking and other domestic purposes such as cooking and laundry, and improvements to drinking water quality through water treatment. It tends to exclude water for productive purposes such as agriculture or energy. 

• Sanitation: Access to and use of facilities and services for the safe disposal of human excreta. It is sometimes, although not usually, extended to refer to other waste aspects such as household solid waste. The term applies to the entire ‘chain’ of services related to excreta disposal from toilet capture and containment through emptying, transport, treatment and final disposal or end use. 

• Hygiene: while the term usually refers to conditions and practices to maintain health and prevent disease, in WASH, hygiene focuses on personal cleanliness, often narrowly on hand washing with soap at critical times such as after toilet use and before cooking or eating. 

These various aspects, separately and as a whole, play a vital role in protecting population health, since inadequate services lead to the spread of harmful pathogens. The most recognised role of WASH for public health is the prevention of infectious diseases, such as diarrhoeal diseases, neglected tropical diseases (see below), vector-borne diseases, and further health consequences such as malnutrition. However, the impact of inadequate WASH on human wellbeing extends to broader aspects such as perpetuating the vicious cycle of disease and poverty, harming educational attainment, and deepening gender and social inequalities.