In this study, we exploit the variation in the timing of tap water connection across villages imposed by the rural drinking water program in China. Using data drawn from the China Family Panel Studies, we find that one additional year of exposure to tap water in early life increases the cognitive test score at ages 10–15 by 0.132 standard deviations. The event study estimates confirm that the beneficial impacts of tap water exposure are concentrated in early life. The mechanism analysis reveals two key channels: improving childhood health and increasing maternal time for childcare. The findings suggest that improving access to tap water has considerable potential to increase rural children’s cognitive skills, and eventually, to narrow the human capital disparity between rural and urban children in China.