This paper investigates the effect of a major water quality improvement program in rural China on the health of adults and children. Using panel data covering about 4500 households from 1989 to 2006, I estimate the impact of introducing village-level access to water from water plants on various measures of health. The regression results imply that the illness incidence of adults decreased by 11 percent and their weight-for-height increased by 0.835kg/m, and that children's weight-for-height and