A twenty-year study in Bangladesh showed that reducing arsenic in drinking water significantly reduces mortality from cancer and heart disease. For participants who switched to safer wells, the level of disease risk matched that of people who were not exposed to arsenic to any great extent. The researchers monitored arsenic exposure using detailed urine testing. The results show that health conditions can improve relatively quickly after switching contaminated water. The study confirms a direct relationship between drinking water quality and the incidence of serious chronic diseases. Reducing arsenic exposure has an immediate positive impact on population health.