Nitrate

How It Works

Nitrate is one of the most common drinking water contaminants in agricultural areas. It enters groundwater from fertilizer application, animal waste, and septic systems. The EPA MCL for nitrate is 10 mg/L (measured as nitrogen). Nitrate's acute health risk to infants makes it one of the most dangerous drinking water contaminants: at elevated levels, it can reduce the blood's ability to carry oxygen, causing potentially fatal "blue baby syndrome." Adults generally tolerate higher levels, but some studies link chronic nitrate exposure to thyroid disease and colorectal cancer. Private wells in agricultural areas are particularly vulnerable — unlike public water systems, private wells are not regulated or routinely tested.

Related Terms

• Maximum Contaminant Level (MCL) — The highest level of a contaminant allowed in drinking water — set by the EPA and enforceable by law. Exceeding the MCL triggers a health-based violation.
• Groundwater — Water found underground in aquifers — the drinking water source for about half of all Americans and nearly all rural residents, generally cleaner than surface water but vulnerable to contamination from agriculture and industry.
• Health-Based Violation — The most serious type of drinking water violation — indicating that water quality has exceeded a maximum contaminant level or failed to meet a treatment requirement that directly protects health.