Agriculture is the primary source of nitrate contamination.
Water utilities in Decatur, Bloomington, Streator, and Pontiac, Illinois all violated the nitrate standard in eight years out of the ten. Danville, Illinois was close behind with seven violations during the same time period. An additional 3.8 million people drink water from private wells that are contaminated above the 10 ppm nitrate standard. While the majority of these systems are still able to provide drinking water that meets the 10 ppm standard, often this comes at significant cost to water utilities and ratepayers. Unlike virtually all other contaminant standards, the 10 ppm federal drinking water standard for nitrate contains no safety factor.