Sources of Nitrate in Drinking Water
Nitrogen is the nutrient applied in the largest quantities for lawn and garden care and crop production. In addition to fertilizer, nitrogen occurs naturally in the soil in organic forms from decaying plant and animal residues. In the soil, bacteria convert various forms of nitrogen to nitrate, a nitrogen/oxygen ion (NO3-). This is desirable as the majority of the nitrogen used by plants is absorbed in the nitrate form. However, nitrate is highly leachable and readily moves with water through the soil profile. If there is excessive rainfall or over-irrigation, nitrate will be leached below the plant's root zone and may eventually reach groundwater.
Nitrate-nitrogen (NO3-N) in groundwater may result from point sources such as sewage disposal systems and livestock facilities, non-point sources such as fertilized cropland, parks, golf courses, lawns, and gardens, or naturally occurring sources of nitrogen. Proper site selection for the location of domestic water wells and proper well construction can reduce potential nitrate contamination of drinking water source.
Indications of Nitrate
Nitrate in water is undetectable without testing because it is colorless, odorless, and tasteless. A water test for nitrate is highly recommended for households with infants, pregnant women, nursing mothers, or elderly people. These groups are the most susceptible to nitrate or nitrite contamination. Nitrate-nitrogen occurs naturally in groundwater, usually at concentrations far below a level of concern for drinking water safety. An initial test of a new water supply is needed to determine the baseline nitrate concentration. Therefore, if the water supply has never been tested for nitrate, it should be tested.
Activities near the well can potentially contaminate the water supply. Domestic wells near potential point sources of contamination, such as livestock facilities or sewage disposal areas, should be tested at least once a year to monitor changes in nitrate concentration. Depending on the location of the well relative to areas where nitrogen fertilizer is applied, follow-up testing to monitor changes from non-point sources may be conducted less often. All drinking water supplies should be checked at least every two or three years to assure that significant increases in nitrogen compounds (nitrate, nitrite, ammonia, and TKN) are not occurring. If a fertilizer or manure spill occurs, the spill should be cleaned up immediately and any wells near the spill should be tested. Unfortunately, any nitrate from the spill may not move through the soil profile quickly and annual testing is recommended to monitor the effects of the spill.