Health Indicator Report of Drinking Water: Nitrates

People drink and use water every day. The majority of Americans are provided with high quality drinking water. About 90% of people in the U.S. get their water from a community water system versus a smaller water supply such as a household well. The U.S. Environmental Protection Agency sets regulations for treating and monitoring drinking water delivered by community water systems. Currently, there are water quality standards and monitoring requirements for over 90 contaminants. Drinking water protection programs play a critical role in ensuring high quality drinking water and in protecting the public's health.

Because people drink and use water every day, contaminants in drinking water have the potential to affect many people. The number of people served by a community water system varies from at least 25 people to hundreds of thousands. Community water systems in the U.S. provide among the highest quality drinking water in the world. However, some contaminants are present at low levels, and it is still possible that drinking water can become contaminated at higher levels. If a person is exposed to a high enough level of a contaminant, they may become ill. Effects can be by the duration (time) of the exposure. Short-term or long-term effects depend on the specific contaminant, the level of contaminant in the water, and the person's individual susceptibility. As additional information is obtained about how specific contaminants affect public health, standards may change in order to better protect public health.

Nitrate (NO3-) originates in drinking water from nitrate-containing fertilizers, sewage and septic tanks, and decaying natural material such as animal waste. Nitrate is very soluble in water, can easily migrate, and does not evaporate (EPA Consumer Fact Sheet). Anthropogenic sources of nitrates are increasing resulting in increased nitrate levels in water resources. Surface water and shallow wells in both rural and urban areas can be affected. Consequently, private wells are especially vulnerable to excess levels of nitrates. Excess levels of nitrate and nitrite can occur in community water supplies. (From the National Environmental Public Health Tracking Network [NEPHTN] Nationally Consistent Data and Measures [NCDM] nitrate indicator document, version 3)

Nitrate and nitrite are nitrogen-oxygen molecules which can combine with various organic and inorganic compounds. Nitrate is the form commonly found in water, often in areas where nitrogen-based fertilizers are used. Short-term health effects from drinking water with nitrate are most harmful to infants under six months of age. This can cause serious illness and sometimes death in this vulnerable population. Long-term exposures to nitrates in the general population may be associated with adverse reproductive problems and some cancers, primarily stomach. Currently nitrate levels are not supposed to exceed 10 milligrams of nitrates per liter of water in order to prevent any nitrate related adverse health effects.

Nitrate was first identified as a public health threat in drinking water in 1945 when high nitrate levels from private wells were shown to cause methemoglobinemia or "blue baby syndrome" in infants who received formula made from well water. When an individual is exposed to nitrate it can be converted to nitrite (NO2-) in the body and then oxidize the ferrous iron (Fe+2) in deoxyhemoglobin in the blood to form methemoglobin containing ferric iron (Fe+3). Methemoglobin cannot transfer oxygen to tissues; thus nitrate or nitrite can starve the body of oxygen and produce a clinical condition known as cyanosis, where the lips and extremities turn gray or blue. Infants younger than four months of age are more sensitive than adults, and can develop "blue baby syndrome" from intake of nitrate higher than 10 mg/L nitrate or 45 mg/L nitrate-nitrogen. Blue baby syndrome is fatal in about ten percent of the cases (ATSDR, 2007). (From the NEPHTN NCDM nitrate indicator document, version 3)

In addition, there is some evidence to suggest that exposure to nitrate in drinking water is also associated with adverse reproductive outcomes such as spontaneous abortions, intrauterine growth retardation, and various birth defects such as anencephaly, related to fetal exposures to nitrate. However, the evidence is inconsistent (Manassaram et al, 2006). (From the NEPHTN NCDM nitrate indicator document, version 3)