WaterAid and healthSafe water, a clean living environment and a clean body are essential for good human health. These basic conditions are often absent in the countries where we work, which has a tremendous effect on the health of communities. A lack of safe water, adequate sanitation and good hygiene practices is directly linked to fatal diseases and conditions such as cholera and diarrhoea. It is linked with many other health problems too, including undernutrition, pneumonia, parasites and blinding trachoma. Most of these diseases are caused by the contamination of drinking water, hands, soil and food with human faeces. The 'F-diagram' - sanitation as a primary barrier between excreta and human contact It is well known that water, sanitation and hygiene (WASH) are important to health and wellbeing for the prevention of infectious disease. This importance has triggered massive investment in public infrastructure and legislation in the wealthiest nations. However, this recognition and investment is largely absent in many low-income countries. By focusing on health in our research, programme and advocacy work, our efforts to improve access to water, sanitation and hygiene are better placed to transform the lives of those we reach. By linking our work to broader national and international efforts to improve health, we also help to draw attention to the importance of WASH in development.