Nitrates in Drinking Water

Nitrate (NO₃) is a compound of nitrogen and oxygen found in nature and in many food items in our diet. Generally, the concentration of nitrates in the ground water is low. The main adult human intake of nitrates is from food rather than from water. Vegetables such as spinach, lettuce, beets and carrots contain significant amounts of nitrate. Drinking water normally contributes only a small percentage of our total nitrate intake.

Although low levels of nitrates may occur naturally in water, sometimes higher levels, which are potentially dangerous to infants, are found. Illinois has adopted a drinking water standard for nitrate of 10 milligrams per liter (10 mg/L) as N (nitrogen). This standard is mandatory for public water supplies and is used as a guide for private water supplies. The U.S. Environmental Protection Agency also uses 10 mg/L as N as a mandatory national standard for public supplies under the Safe Drinking Water Act. The 10 mg/L standard expressed as nitrogen (N) is equivalent to 45 mg/L expressed as nitrate.

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 waste water, refuse dumps, animal feedlots, septic tanks and private sewage disposal systems, urban drainage and decaying plant debris. Geologic formations and direction of ground water flow also may influence nitrate concentration.

High nitrate levels in drinking water pose a health risk to infants because they may cause methemoglobinemia, a condition known as “blue baby syndrome.”

High nitrate levels interrupt the normal body processes of some infants. Nitrate becomes toxic when it is reduced to nitrite, a process that can occur in the stomach as well as in the saliva. Infants are especially susceptible because their stomach juices are less acidic and therefore are conducive to the growth of nitrate-reducing bacteria. (Adults can consume large quantities of nitrates in drinking water or food with no known ill effects; their stomachs produce strong acids that do not promote the growth of bacteria that convert nitrate to nitrite.) Nitrite in the blood combines with hemoglobin to form methemoglobin, which reduces the capability of the blood to carry oxygen to all parts of the body. This results in the “blue” condition of the baby’s skin.

Infants younger than 6 months of age are most susceptible. However, because of individual differences in infants, some may not be affected. If an infant is affected, the skin turns a blue color, similar to the color of the blood vessels located close to the skin. If a parent or other caregiver observes this condition, medical help should be sought immediately. The infant is being asphyxiated because oxygen cannot be transported by the blood. Prompt medical attention normally results in quick recovery of the infant.

In all cases where drinking water contains more than 10 mg/L of nitrate as nitrogen, an alternative source of water should be found for the infant. Boiling the water will not reduce the nitrate concentration; in fact, it actually increases the concentration by evaporating off the water and leaving the nitrates behind. Water that is high in nitrates should not be used for preparing infant formula or in any other way that could result in consumption by a baby.

Federal and state regulations require the testing of public water systems for nitrates; however, high nitrate concentrations can occur in private water wells. If infants will be consuming water from a private water well, the water should be tested for nitrates as well as for bacteria. To arrange for bacteriological and nitrate analyses of your drinking water or if you have questions concerning safe drinking water, contact your local health department or the nearest Illinois Department of Public Health regional office.

Updated Dec 2010