Abstract
About 1 in 15 babies in Aotearoa New Zealand (NZ) are born “preterm” (before 37 weeks of gestation). Emerging evidence suggests nitrate in drinking water may increase the risk of preterm birth at levels well below the current regulatory limit (11.3 mg/L). In a newly published peer-reviewed study (https://doi.org/10.1016/j.envres.2026.125169), we analysed more than 700,000 singleton birth records in NZ, linking gestational age with estimated nitrate concentrations in drinking water at the mother’s usual residence.
The risk of preterm birth increased by about 1% per 1mg/L increase in nitrate exposure. As an observational study, the findings do not prove causality but are consistent with previous large cohort studies in other countries. If the relationship is causal, nitrate exposure could contribute to around 4% of preterm births nationally each year. The increased risk is likely to be small for most populations served by a community drinking water supply, but could be more substantial for those relying on private ground water supplies for which nitrate pollution is a known problem in parts of NZ. The NZ Government needs to reassess regulatory limits for nitrates in drinking water based on this new evidence and from evidence that has prompted the Government of Denmark to commit to setting lower limits. Both central and local government in NZ need to give greater emphasis on the protection of the quality of drinking water at source, which will reduce both nitrate pollution and microbiological contamination of water supplies.