This research will investigate the association between nitrate in drinking water and preterm births. We will conduct a retrospective cohort study using a national cohort of births from 2009-2021 (~700,000) to assess the impact of prenatal exposure to nitrate in drinking water on preterm births. We will also include a within-mother study design where only consecutive children from the same mother are included in the analysis providing additional control for confounding by maternal factors. We will use the Integrated Data Infrastructure (IDI) to build the cohort and provide individual-level data on key confounders. Nitrate exposure via drinking water will be assessed through collation of testing results and spatial data on water supply boundaries from registered water supplies. Nitrate concentrations for all unregistered supplies will be modelled using existing environmental monitoring, geophysical and land-use datasets.