Nitrate is a chemical from fertilizers and waste that enters water through agricultural runoff. It's especially harmful to infants, causing oxygen deficiency in the blood.

Nitrate, measured in parts per million (ppm), primarily enters groundwater through soil absorption from agricultural fertilizers, septic systems, and animal waste. The EPA regulates nitrate levels in drinking water due to its health risks, particularly for infants. Excessive nitrate can lead to methemoglobinemia, or "blue baby syndrome," where the blood's oxygen-carrying capacity is reduced. While nitrate is a natural part of the nitrogen cycle, human activities have significantly increased its presence in water sources.