What are the links between changes in population and the availability of water? Do people move house to obtain better water supplies? How do urban migrants cope with water shortages? Research at the London School of Tropical Hygiene and Medicine tries to answer these questions using a case study in Mwanza, northern Tanzania. Water shortages contribute to poor agriculture performance, which causes out migration from rural areas. But moving to urban areas often fails to solve people’s water problems: new migrants often settle where water provision is poor; they also lack the social networks of settled inhabitants, who can obtain water from each other. Even if human populations decrease, problems of resource access will continue to escalate, the study suggests, unless both consumption and distribution issues are addressed.