The burden of disease attributable to water, sanitation and hygiene can be expressed as : Number of deaths Death rate Number of DALYs DALYs rate Disability -Adusted Life Years (or DALYs) are a summary measure of population health that combine (i) the years of life lost as a result of premature death and (ii) the years lived with a disease. Death and DALY rates are calculated by dividing the number of deaths, resp. DALYs, by the total population (or indicated if a different population group is used, e.g. children under 5 years). Evidence from epidemiological studies have shown that exposure to unsafe water, sanitation and hygiene habits is, among others, directly linked to diarrhoeal diseases. In this estimate, onlt the impact of diarrhoeal diseases is taken into account.