Nitrate and nitrite are nitrogen compounds from fertilizers and waste that can seep into water sources. High levels pose health risks, especially for infants.

Nitrate and nitrite enter water sources primarily from agricultural runoff, septic systems, and animal waste. They seep through soil into groundwater, making well water particularly vulnerable. These compounds are measured in milligrams per liter (mg/L) or parts per million (ppm). Nitrate can convert to nitrite in the environment and human body. The EPA sets limits of 10 mg/L for nitrate and 1 mg/L for nitrite to protect public health, particularly infants who are at risk of methemoglobinemia (blue baby syndrome) from high levels.