In 1854, in the Soho district of London, cholera swept through the population. The physician John Snow investigated the cause of the outbreak and hypothesized that it was due to contaminated water. So began the field of epidemiology. Today's episode focuses on water quality, sanitation and disease. My guest is Dennis Warner, who has worked for forty years in the field of water supply and sanitation, including for Catholic Relief Services, the Peace Corps, the University of Dar es Salaam, Duke University, the World Health Organization, the World Bank, and the United States Agency for International Development.