Nitrate in Drinking Water
Historical and current water quality monitoring shows that nitrate is present in groundwater throughout much of Nebraska. It is when results are at or above the 10mg/L Maximum Contaminant Level (MCL) that hazardous health effects become a concern among humans and animals. Nitrate is colorless, odorless, and tasteless and the only way it can be detected in drinking water is through submitting a sample for laboratory testing.
Where Does Nitrate Come From and What is Nitrification?
Nitrogen is the nutrient applied for lawn and garden care and crop production to increase productivity. Feedlots, animal yards, septic systems, and other waste treatment systems are additional sources of nitrogen that is carried in waste. Nitrogen occurs naturally in the soil in organic forms from decaying plant and animal material.
Bacteria in the soil convert various forms of nitrogen to nitrate, a nitrogen/oxygen ion. This process is called nitrification. A good example of nitrification is when bacteria within the soil converts the ammonia from a fertilizer into nitrite and then into nitrate. This is desirable since the majority of the nitrogen used by plants is absorbed in the nitrate form. However, nitrate is highly soluble and readily moves with water through the soil profile. If there is excessive rainfall or over-irrigation, nitrate will move below the plant’s root zone due to soil saturation and may eventually reach groundwater.
How We Ingest Nitrate and Potential Health Hazards
We ingest nitrates through the vegetables we eat, particularly leafy greens, and potentially through the water we drink. Nitrates in our groundwater going undetected is more of a concern with private drinking water wells because they are often not tested regularly, whereas public water supplies are on a strict testing schedule. The acute health hazard associated with nitrate-contaminated drinking water that exceeds the 10mg/L Maximum Contaminant Level (MCL) occurs when bacteria in the human or animal digestive system transform nitrate to nitrite. The nitrite reacts with iron in the blood’s hemoglobin, the substance in red blood cells that carries oxygen, to form methemoglobin. This creates the condition known as methemoglobinemia (often referred to as “blue baby syndrome”), in which due to the nitrites, blood lacks the ability to carry sufficient oxygen to the individual body cells. Infants under one year of age have the highest risk of developing methemoglobinemia. An older person who has a gastrointestinal system disorder resulting in increased bacteria growth may also be at greater risk than the general population. In addition, an individual who has a genetically impaired enzyme system for metabolizing methemoglobin may be at greater risk as well. The general population has a low risk of developing methemoglobinemia, even when ingesting relatively high levels of nitrate/nitrite. Other health effects from long-term consumption of water containing varying concentrations of high nitrate continue to be researched.
Testing public water supplies for nitrate is required under the federal Environmental Protection Agency (EPA) Safe Drinking Water Act. The EPA Maximum Contaminant Level (MCL) for public water supplies is measured and reported as nitrate-nitrogen, (NO3-N), which is the amount of nitrogen in the nitrate form. The MCL for nitrate-nitrogen in a public water supply is 10 milligrams per liter (mg/L) which also can be expressed as 10 parts per million (ppm).
While there are no federal or state laws regarding the testing of private well water, the contaminant MCLs from the Safe Drinking Water Act are used. It is highly recommended that an owner of a private well test their water for nitrates and bacteria annually. While do-it-yourself test kits are available, the results from these are considered to be more of a screening tool, not definitive like what a laboratory test will give. Because private well water is every bit as important as public drinking water, it is also highly recommended to order a test kit from an accredited laboratory. This simply means that the laboratory is accredited by the State of Nebraska Public Health Environmental Laboratory to conduct the testing of public water system samples mandated under the Safe Drinking Water Act. By doing this you will have the assurance that your water sample is being tested in the same way public water sample is.
Concerns of Nitrate in Private Wells
If one has a new private well, initial nitrate and bacteriological tests by an accredited laboratory should be conducted to determine the baseline nitrate concentration in the water source. This is particularly important for households with infants, pregnant women, nursing mothers, elderly people, or anyone with a compromised immune system. These groups are believed to be the most susceptible to nitrate health effects if they consume drinking water over the 10mg/L MCL. Livestock and pets within the same groups can also be negatively affected by high nitrate concentrations.
Activities at or near a well site can potentially contaminate the water supply, changing the nitrate concentration over time. In order to monitor for changes it is highly recommended that private drinking water wells be tested for nitrates and coliform (bacteria) annually, as well as any other contaminants of concern in your area.
What to Consider if Nitrates in Your Water Source Exceed the 10mg/L MCL
If nitrate-nitrogen exceeds the 10mg/L MCL, you should voluntarily consider an alternative drinking water source or water treatment. Decisions should be based on a nitrate analysis by a reputable laboratory, and after consulting with a physician to help evaluate the level of risk. One will need to use bottled water for preparing infant formula and cereal, as well as for drinking and cooking until such time that a more permanent solution is in place. It may be possible to obtain a satisfactory alternate water supply by drilling a new well in a different location or a deeper well in a different aquifer, but there are no guarantees. Many choose drinking water treatment as an alternative. There are three treatment methods that can be implemented to remove or reduce nitrate-nitrogen in drinking water: distillation, reverse osmosis, and ion exchange.
Carbon filters and standard water softeners are common among households for drinking water treatment, but they do not remove or reduce nitrate-nitrogen, nor does boiling water on the stove top. In fact, when water is boiled, water is lost through evaporation, but the nitrates remain behind. This results in an increased nitrate-nitrogen concentration in the water that remains after prolonged boiling.
For further information on nitrates, take a look at NebGuide G1784, “Drinking Water: Nitrate-Nitrogen” at https://extensionpublications.unl.edu/assets/pdf/g1784.pdf. If you would like to find out what laboratories are accredited for drinking water analysis in Nebraska, you can go to the Nebraska Public Health Environmental Lab website, http://dhhs.ne.gov/Pages/Public-Health-Lab.aspx. If you wish, you can order a nitrate and/or coliform (bacteria) test kit from here or you can call the Lab at 402-471-3935. The Nebraska Public Health Environmental Laboratory is located at 3701 South 14th Street, Lincoln, NE 68502. There is a charge for these tests, please ask for current prices.
*This article contains some content originally written in 2011 by Sharon Skipton, retired Extension Educator.
This article was reviewed by Bruce Dvorak