Most nitrogenous materials in natural waters tend to be converted to nitrate, so all sources of combined nitrogen, particularly organic nitrogen and ammonia, should be considered as potential nitrate sources. Primary sources of organic nitrates include human sewage and livestock manure, especially from feedlots. The primary inorganic nitrates which may contaminate drinking water are potassium nitrate and ammonium nitrate both of which are widely used as fertilizers. According to the Toxics Release Inventory, releases to water and land totaled over 253 million pounds in 2012. The US EPA conducted a 6-year review for selected drinking water contaminants, and from 1998-2005 the largest releases of nitrates occurred in California by far. In 2005 alone, of the data collected for the review, California had 320 systems above the MCL. The principle sources of nitrate contamination in water are thus fertilizers, animal waste, and septic tank wastes. The water supplies most vulnerable to nitrate contamination are in agricultural areas and in well waters having a close or hydraulic relationship to septic tanks.
