Nitrates in Well Water

Nitrates are found in fertilizers, manure and liquid waste, and naturally occurring soil bacteria can convert other forms of nitrogen to nitrate.  The water quality standard in Pennsylvania for nitrates is 10 parts per million (ppm).  However, there are no state regulations on private wells in Pennsylvania so the responsibility of monitoring water quality of private wells is up to the home owner.  Lancaster County is known to have high nitrate levels with 10-20% of wells having nitrate levels above the 10 ppm limit with 30-60% of wells in limestone areas measuring high in nitrates.  

The health concerns with nitrates apply to both humans and animals.  Nitrate is converted to nitrite by bacteria in the digestive track of people and animals.  Once the nitrite form is absorbed it decreases the ability of red blood cells to carry oxygen.  The higher the nitrate level in the water the more dangerous it becomes.  Babies are especially vulnerable because they do not produce a lot of acid in their stomachs; therefore, nitrate to nitrite converting bacteria can grow in the stomach and produce more nitrite compared to a more acidic stomach.  Adults, with their highly acidic stomachs, do not have nitrate to nitrite converting bacteria in their stomachs so nitrate is only converted to nitrite once it reaches the large intestine at which point there is less opportunity for absorption before it is excreted.

Ruminant are the most susceptible group of animals on the farm due to the bacteria population in the rumen that converts nitrates to nitrites.  Nitrites are then absorbed across the rumen wall and inhibit oxygen transport.  Nitrates are found naturally in ruminant feed so high nitrate water may push them past the toxicity level.  Acute toxicity can be treated and animals can recover well if caught early, but there is some concern about chronic impacts of slightly high nitrate levels.  A University of Wisconsin study showed that, over time, the services per conception were higher in cows given high nitrate water versus cows given water with no nitrates.  

Although there are ways to treat high nitrate wells, preventing nitrate contamination of the well in the first place is the best option.  Careful manure application is the best way to prevent nitrate contamination of well water.  Manure contains nitrogen in the form of ammonia, nitrates, and organic nitrogen.  Ammonia can be converted to nitrates by soil bacteria.  Nitrates are associated with the water in the soil and leach down through the soil if not utilized by the crop.  Once the nitrates are below the root zone they are no longer available to the plants and will continue down through the soil until they reach ground water.  Once in ground water nitrates remain unchanged and can build up over time.  Therefore, applying nitrogen to meet the demands of the crop without over applying is important to prevent nitrate leaching into ground water.  Spreading of manure near shallow wells, poorly sealed or constructed wells, and wells that draw from shallow aquifers should be avoided as these wells are at greatest risk for nitrate contamination because the path for manure nitrate to the ground water is the least restricted.  Also, wells should be located away from sources of contamination like barnyards, fields that receive manure, septic fields, etc.  Wells should also be sealed properly to prevent contamination from surface water.