Nitrate at the tap: Des Moines Metro drinking water

Daily readings from the Fleur Drive Treatment Plant. Shaded zones mark thresholds where peer-reviewed research first observes elevated cancer risk. All below the 1962 EPA limit.

How to read this: Risks are cumulative. If your water is above the colorectal threshold, that risk applies. If it's also above the thyroid threshold, both apply. Crossing a higher line never replaces the risks identified at lower levels. It adds to them.

Research cited 7 peer-reviewed studies

1. Schullehner et al. 2018. 1.7 million Danes, 33-year follow-up. Elevated colorectal cancer risk observed at nitrate concentrations starting around 0.87 mg/L NO₃-N. Int. J. Cancer. PubMed 29435982
2. Erichsen et al. 2025. Danish Diet, Cancer and Health Cohort. 52% higher colon cancer rate at water nitrate ≥2.1 mg/L NO₃-N. Environment International. PubMed 40628182
3. Ward et al. 2010. Iowa Women's Health Study, 21,977 women. Thyroid cancer risk elevated at nitrate >2.46 mg/L; risk more than doubles after 5+ years above 5 mg/L NO₃-N. Epidemiology. Free full text
4. Inoue-Choi et al. 2015. Iowa Women's Health Study, 28,555 women. Ovarian cancer risk doubled at water nitrate ≥2.98 mg/L NO₃-N. Int. J. Cancer. Free full text
5. Donat-Vargas et al. 2023. MCC-Spain. Long-term water nitrate >3 mg/L NO₃-N linked to prostate cancer, particularly aggressive tumors. Environmental Health Perspectives. PubMed 36883836
6. Jones et al. 2016. Iowa Women's Health Study, 34,708 women. Bladder cancer risk 62% higher after 4+ years of water >5 mg/L NO₃-N. Environmental Health Perspectives. Free full text
7. Jones et al. 2017. Iowa Women's Health Study, 15,577 women. Kidney cancer risk 2.3x higher at water nitrate ≥5 mg/L NO₃-N vs. lowest quartile. Epidemiology. Free full text

The EPA's 10 mg/L limit was set in 1962 to prevent infant methemoglobinemia ("blue baby syndrome"); cancer endpoints were not evaluated. Studies listed show association, not proof of causation. Source data: Des Moines Water Works (dmww.com).