Nitrate in Wisconsin Drinking Water

Nitrate enters groundwater from row-crop fertilizer, dairy manure spreading, and septic systems. The EPA limit is 10 mg/L (measured as nitrogen) because levels above that can cause methemoglobinemia — 'blue baby syndrome' — in infants under six months old. The risk is acute, not chronic: a single bottle of formula made with high-nitrate water can be dangerous for an infant. Adults are not at the same immediate risk, but long-term exposure has been linked to thyroid disease and certain cancers in epidemiological studies.

In Wisconsin, the heaviest nitrate burden falls on private well users in the central and southwestern parts of the state — Kewaunee, Wood, Portage, Marathon, and the Driftless Area. Municipal systems in agricultural counties also struggle with it; some have installed ion exchange treatment, others blend cleaner wells. Unlike radium, nitrate is partly preventable through farm management, which is why it's an ongoing political fight in the state legislature.