Birth outcome effects of nitrate contamination in drinking water

Despite the prevalence of drinking water contamination in the United States, its health effects are not well understood. Unlike the extensive research on health impacts of air pollution, studies on water contamination are limited, mainly due to a lack of high-frequency water contamination data. To address this gap, I construct a novel dataset of monthly nitrate contamination levels in California’s community water systems linked with individual birth records. Nitrate contamination is a persistent issue in water systems in the United States, posing a potential threat to infant health. This study estimates the effect of prenatal exposure to nitrate contamination below current regulatory limits on birth outcomes. Using a panel fixed-effects approach with water system and time fixed effects, I compare birth outcomes across infants from the same water system who were exposed to differing levels of nitrate contamination during each trimester of gestation. I find that second-trimester exposure to nitrate concentrations below regulatory limits increases the likelihood of preterm birth and low birth weight by 1.2 and 1 percentage point, respectively. Relative to sample means, these estimates translate to a 15 % increase in the probability of preterm birth and a 17 % increase in the probability of low birth weight birth. Results further suggest that lowering the current regulatory limit below 5 mg/L (half the current limit) could prevent nitrate-related adverse birth outcomes.