Each year, diarrhea kills an estimated 1.8 million people worldwide. More than 90 percent of the victims are children younger than five in developing countries. This research project assessed the prevalence of diarrhea in the developing world through multiple exposure routes: water supply, sanitation and hygiene practices. The initial research focused on the largest city in Tanzania, Dar es Salaam, where historically residents have relied on water from shallow wells in close proximity to household pit latrines. The project brought together investigators and research methods from environmental science and engineering, medicine, public health, urban planning and policy to identify promising, cost-effective approaches to reducing childhood mortality from water and sanitation-related diseases.