Nitrate is present in high levels in wastewater due in part to the high nitrates present in human sewage but also from some types of industrial effluent entering the municipal sewer system.
Nitrate is also a very common contaminant in both surface water and ground water. Nitrate occurs naturally in source water as a result of decaying plants. However, there are other manmade sources of nitrate than can increase the presence of nitrate in source waters to dangerous levels. Agricultural sources of nitrates include livestock excrement and chemical fertilizers.