Although the quality of ground water in Idaho is generally good, ground water quality monitoring shows that in specific areas of the state, Idaho's ground water has been significantly degraded. This localized degradation negatively impacts water quality and potentially threatens domestic water supplies, aquaculture, agriculture, mining, industrial, and other ground water beneficial uses.

Nitrate is one of the contaminants responsible for this degradation and is one of the most widespread ground water contaminants in Idaho. Nitrate is a form of nitrogen, an element whose compounds are vital components of foods and fertilizers. It is an essential nutrient for plant growth. Nitrate comes from a variety of sources, such as plants and other organic matter that return nitrate to the soil as they decompose. Septic sewer systems, waste from animal feedlots, and nitrogen-based fertilizers also discharge nitrates to the environment.

Nitrate that is not used by plants can build up in and move through the soil. Precipitation, irrigation, and sandy soils allow nitrate to move around and find its way into surface water and ground water.

While nitrate is just one of the potential ground water contaminants in Idaho, more is known about nitrate in ground water in Idaho than other contaminants. In addition, the presence of nitrate is a good indicator of other potential water quality problems.

Ground water supplies 95% of the water used in Idaho households and provides drinking water to more than 200 Idaho cities and towns. High levels of nitrate in drinking water are associated with adverse health effects.

The U.S. Environmental Protection Agency has established a federal drinking water standard of 10 milligrams of nitrate per liter of water (10 mg/L). The Idaho ground water quality standard is also 10 mg/L. Of wells sampled in Idaho for nitrate, 3% have nitrate concentrations above 10 mg/L and 30% have nitrate concentrations between 2 and 10 mg/L.

People can be exposed to nitrate through food and water. In most populations, short-term exposure to even fairly large amounts of nitrate produces no immediate health effects. However, sensitive populations (babies, people in poor health, and the elderly) can be susceptible to problems from short-term nitrate exposure. Infants younger than six months of age are especially sensitive to nitrate poisoning, which may result in serious illness or death. The illness occurs when nitrate is converted to nitrite in the baby's body. Nitrite reduces the amount of oxygen in the baby's blood, causing shortness of breath and blueness of the skin (the illness is often called "blue baby syndrome"). The technical term for this condition is "methemoglobinemia." This illness can cause the baby's health to deteriorate rapidly over a period of days.

Livestock, such as cattle and sheep, also can be poisoned by high levels of nitrate in their water. It is recommended that water with a concentration of over 100 mg/L not be given to livestock.

Public water systems are required to sample for various contaminants, including nitrate, on a regular basis. If you are connected to a public water system, refer to that system's Consumer Confidence Report for the nitrate level in your drinking water. The contact information for your local water system should appear on your water bill, or you can contact your regional DEQ office for that information.

Nitrate sampling is not required for domestic or stock wells. However, DEQ recommends that owners test their wells for nitrate on a regular basis. To find out if your domestic or stock well water contains nitrate, have it tested by a laboratory certified for nitrate testing. Read more about recommended tests for private wells. It is particularly important to test for nitrate if you live in a nitrate priority area.

As part of DEQ's goal of restoring degraded ground water, DEQ has developed a list of degraded ground water areas. This list focuses on nitrate and ranks the top 32 nitrate-degraded areas (referred to as "nitrate priority areas") in the state based on the severity of the degradation; the rank of "1" indicates the most severely impacted area in the state.

The data used to rank the priority of the areas are updated on a continual basis. DEQ uses a specific nitrate priority ranking process, described in the  2008 Nitrate Priority Area Delineation and Ranking Process document (pdf 4.4 mb, 108 pages) that was developed by the Ground Water Monitoring Technical Committee, as the basis for the ranking. Areas are ranked based on criteria such as population, existing water quality, water quality trends, and other factors. The process also takes into account impacts on beneficial uses other than water supply. The nitrate priority area ranking was originally released in 2002 and updated in 2008.

An interactive mapping application of the nitrate priority areas with nitrate concentrations of wells monitored by DEQ, the Idaho Department of Water Resources in conjunction with the U.S. Geological Survey, and Idaho State Department of Agriculture has been created. Public water system well locations are not displayed for security reasons. Capture zones delineated for source water assessments are an optional layer that may be turned on when zooming into an area on the map.

> Link to interactive mapping application. 

If you own a well and live in one of the nitrate priority areas, it is particularly important to test your well water on a regular basis. If your well is not in a nitrate priority area, this does not rule out the potential for nitrate contamination, so testing your well water is still recommended. more for well owners

This nitrate priority area ranking is used to prioritize the development and implementation of strategies to help reduce nitrate loading from land-use activities. In coordination with other agencies, DEQ assists local ground water quality advisory groups in developing ground water quality management strategies for nitrate priority areas. View a map (pdf 1.5 mb, 1 page) of the status of ground water management plans or contact your local DEQ regional office to learn if a plan is underway in your area and how you can become involved. Completed plans area available on DEQ's Ground Water Reports page.

(DEQ Publication, January 2001: pdf 107 kb, 9 pages)

Idaho's Ground Water Quality Rule (IDAPA 58.01.11)

(pdf on Department of Administration Web site)

DEQ's Final 2002 Nitrate Priority Area Ranking

(DEQ Publication, 2002: pdf 411 kb, 4 pages)