We study the effect of in utero exposure to treated tap water on childhood health in rural China, where boiling water to inactivate disease-causing microorganisms before drinking is common. We exploit the gradual rollout of a rural drinking water program that supplies treated tap water to households. Besides microorganisms, the treatment removes chemical pollutants. We find that exposure to treated tap water in utero increases height at ages 1–11 by 0.3 standard deviations. We also document improvements in other health outcomes at different stages of childhood, as well as a reduction in the incidence of non-waterborne digestive diseases. Improving health by age one and inducing more health investments from parents are two possible channels. Results highlight the importance of removing chemical pollutants from drinking water to protect fetuses from environmental insults.