Nitrates in Drinking Water

Nitrate (NO3), is a chemical form in which the element nitrogen usually appears in groundwater. Water naturally contains less than 1 milligram of nitrate-nitrogen per liter and is not a major source of exposure. Higher levels indicate that the water has been contaminated and are potentially dangerous to infants. The U.S. Environmental Protection Agency (EPA) and the Indiana Department of Environmental Management (IDEM) use a standard of 10 milligrams per liter (mg/l) as the maximum concentration of nitrate, expressed as total nitrogen, that is allowed in the water delivered by a public supply to its customers. This mandatory standard for public supplies is used as a guide for private residence water supply samples.

It is often difficult to pinpoint sources of nitrates because there are so many possibilities. Sources of nitrogen and nitrates may include runoff or seepage from fertilized agricultural lands, municipal and industrial wastewater, refuse dumps, animal feedlots, failing septic systems, urban drainage and decaying plant debris. The geologic formations and directions of ground water flow influence the potential for nitrate contamination from a particular source. The closer the well is to the source of nitrogen or nitrate, the greater the likelihood that elevated levels of nitrate could occur. Also, shallow, less than 50 feet deep, water wells are more prone to experiencing higher nitrate concentrations.

Health Concerns
Since 1945, health officials have known that high nitrate levels in drinking water pose a risk to infants. Infants who are fed water or formula made with water that is high in nitrate can develop a condition that doctors call methemoglobinemia. The condition is also called "blue baby syndrome" because the skin appears blue-gray or lavender in color. This color change is caused by a lack of oxygen in the blood.

Nitrate to Nitrite
Normal body processes of some infants are interrupted by high nitrates. The toxicity of nitrate occurs due to the reduction of nitrate to nitrite, a process that can occur in the stomach as well as in the saliva. Nitrite acts in the blood to change the hemoglobin to methemoglobin, which reduces the capability of the blood to perform as an oxygen carrier to the tissues. Because oxygen cannot be transported with the body's blood vessels, the body becomes asphyxiated causing the skin to become blue, similar to the color of the blood vessels located close to the skin.

All infants under 6 months of age are at risk of nitrate poisoning. Some babies may be more sensitive that others. Infants suffering from "blue baby syndrome" need immediate medical care because the condition can lead to coma and death if it is not treated promptly.

Nitrate in Breast Milk
When nursing mothers ingest water that contains nitrate, the amount of nitrate in breast mike may increase. Although no confirmed cases of "blue baby syndrome" have been associated with nitrate in breast milk, it may be advisable for nursing women to avoid drinking water that contains nitrate levels more than 10 milligrams per liter nitrate-nitrogen.

Adults can consume large quantities of nitrates in drinking water or food with no obvious ill effects. However, a lifetime exposure to nitrates or nitrites at levels above the maximum contaminant level can lead to diuresis. Diuresis is an increase of starchy deposits and hemorrhaging of the spleen. 1 People who have heart disease, lung disease, certain inherited enzyme defects, or cancer may be more sensitive to the toxic effects of nitrate than others.

Recommended Precautions
When water with nitrate exceeding 10 mg/l (NO3 as N) has been discovered, remember: Do not give water to infants under 6 months of age either directly or in prepared infant formula. Use only a safe water from a known low nitrate source. Do not boil high nitrate water to reduce the nitrate level. Boiling water high in nitrates actually increases the nitrate due to evaporation of the water. Adults should limit their daily intake if diagnosed with chronic health problems that may increase your sensitivity to nitrate, or if you are concerned about scientific uncertainty regarding the health effects of long-term exposure to nitrate contaminated water.

Testing for Nitrate
The only way to determine the nitrate level in water is to have a water sample tested by a certified laboratory. Public water supplies are tested regularly for the presence of nitrate. A nitrate test is recommended for all newly constructed private wells and wells that have not been tested during the past 5 years. Testing is also recommended for wells used by pregnant women and is essential for wells that serve infants under 6 months of age.

Take Care When Reporting
Be careful in interpreting your water test results. Nitrate concentration can be reported either as nitrate (NO3) or as nitrate-nitrogen (NO3-N). Be sure to know which reporting system is being used since the acceptable concentrations of each are considerable different. If the lab reports its results as nitrate-nitrogen (NO3-N), the drinking water quality standard is 10 milligrams per liter (mg/l). The standard is 45 milligrams per liter (mg/l) if the results are reported as nitrate (NO3). A milligram per liter (mg/l) is also equal to a part per million (ppm). If you are unsure of how to interpret the report, contact the lab, or your local health department. It is important to check the lab report carefully because the 2 systems of reporting are frequently interchanged.

Frequency of Tests
Wells with nitrate-nitrogen levels below 5 mg/l should be retested every few years. If the levels are between 5 - 10 mg/l, owners should consider testing more often to check for seasonal changes. Additional testing may also be useful if there are known sources of nitrate or if high nitrate levels are detected in nearby wells.

Treatment Solutions
Nitrate is a very soluble substance, easily dissolved in water and extremely hard to remove. Treatment for nitrate is, therefore, very complicated and expensive. However, only water used for drinking and cooking needs to be treated. Three methods for treating water with equipment in your home to reduce or remove nitrates are:
  • Blending
  • Demineralization by distillation or reverse osmosis
  • Ion exchange
There is no simple way to remove all nitrate from your water. Although it is common to think of boiling, softening, or filtration as a means of purifying water, none of these methods reduce nitrate contamination. Boiling water is, in fact, the worst thing to do because it actually increases the concentration of the nitrate. Softening and filtration do nothing at all to remove nitrate contamination.