Nitrate: Health Effects in Drinking Water
CORNELL COOPERATIVE EXTENSION
Nitrate: Health Effects in Drinking Water
Margaret McCasland, Nancy M. Trautmann, and Keith S. Porter
Center for Environmental Research
Robert J. Wagenet
Dept. of Agronomy
Nitrate is one of the most common groundwater contaminants in rural areas. It is
regulated in drinking water primarily because excess levels can cause
methemoglobinemia, or "blue baby" disease. Although nitrate levels that affect
infants do not pose a direct threat to older children and adults, they do
indicate the possible presence of other more serious residential or agricultural
contaminants, such as bacteria or pesticides.
Nitrate in groundwater originates primarily from fertilizers, septic systems,
and manure storage or spreading operations. Fertilizer nitrogen that is not
taken up by plants, volatilized, or carried away by surface runoff leaches to
the groundwater in the form of nitrate. This not only makes the nitrogen
unavailable to crops, but also can elevate the concentration in groundwater
above the levels acceptable for drinking water quality. Nitrogen from manure
similarly can be lost from fields, barnyards, or storage locations. Septic
systems also can elevate groundwater nitrate concentrations because they remove
only half of the nitrogen in wastewater, leaving the remaining half to percolate
This bulletin focuses on the health effects of nitrate in drinking water, and
another bulletin in this series (Fact sheet 400.04, Groundwater: What It Is and
How to Protect It), addresses ways of protecting the quality of groundwater
What Is Nitrate?
Nitrate is an inorganic compound that occurs under a variety of conditions in
the environment, both naturally and synthetically. Nitrate is composed of one
atom of nitrogen (N) and three atoms of oxygen (O); the chemical symbol for
nitrate is NO3. Nitrite (NO2) can be formed from nitrate by a chemical process
called reduction. Nitrate does not normally cause health problems unless it is
reduced to nitrite.
Nitrate in drinking water is measured either in terms of the amount of nitrogen
present or in terms of both nitrogen and oxygen. The federal standard for
nitrate in drinking water is 10 milligrams per liter (10 mg/l) nitrate-N, or 45
mg/l nitrate-NO3. when the oxygen is measured as well as the nitrogen. Unless
otherwise specified, nitrate levels usually refer only to the amount of nitrogen
present, and the usual standard, therefore, is 10 mg/l.
Short-term exposure to drinking water with a nitrate level at or just above the
health standard of 10 mg/l nitrate-N is a potential health problem primarily for
infants. Babies consume large quantities of water relative to their body weight,
especially if water is used to mix powdered or concentrated formulas or juices.
Also, their immature digestive systems are more likely than adult digestive
tracts to allow the reduction of nitrate to nitrite. In particular, the presence
of nitrite in the digestive tract of newborns can lead to a disease called
Infant Feeding Practices to Minimize Intake of Nitrate and Nitrite
- Breast feeding. Little if any nitrate gets into breast milk, unless the mother
is consuming very large quantities of nitrate. Also, bacterial contamination is
not a problem when breast milk is consumed directly.
- Bottle feeding. Use already diluted liquid formulas or use low-nitrate water to
dilute concentrated liquid or powdered formulas. Also, mixed formulas should be
kept under refrigeration and used promptly to minimize bacterial reduction of
nitrate to nitrite.
- Vegetables. Since many vegetables are high in nitrate, their consumption should
be limited until an infant is 4-6 months old and their digestive tract has
sufficiently matured. Your physician can help you decide when to add new foods.
Vegetables should always be prepared while fresh and refrigerated promptly after
cooking to minimize bacterial activity.
What Is Methemoglobinemia?
Methemoglobinemia is the most significant health problem associated with nitrate
in drinking water. Blood contains an iron-based compound called hemoglobin,
which carries oxygen. When nitrite is present, hemoglobin can be converted to
methemoglobin, which cannot carry oxygen. In the blood of adults, enzymes
continually convert methemoglobin back to hemoglobin, and methemoglobin levels
normally do not exceed 1 percent. Newborn infants have lower levels of these
enzymes, and their methemoglobin level is usually 1 to 2 percent. Anything above
that level is considered methemoglobinemia.
Few clearcut symptoms are associated with methemoglobin levels between 1 and 10
percent. At higher levels, symptoms of cyanosis usually appear. Babies with this
condition have bluish mucous membranes and may also have digestive and
respiratory problems. At methemoglobin levels above 20 to 30 percent, the
primary effects result from the blood's severely reduced oxygen-carrying
capacity and are referred to as anoxia. At methemoglobin levels around 50 to 70
percent, brain damage or death can occur.
Once diagnosed, methemoglobinemia can be readily reversed, although with anoxia
permanent damage may have occurred. Methemoglobinemia can be prevented by
restricting consumption of nitrite and nitrate and by limiting the opportunities
bacteria have to reduce nitrate in food to nitrite before consumption.
Consuming drinking water with nitrate levels near the drinking water standard
does not normally increase the methemoglobin level of humans beyond infancy.
Some individuals, however, may have increased susceptibility to
methemoglobinemia due to exposure to antioxidant medications and chemicals, or
other conditions that may inhibit the body's ability to reconvert methemoglobin
to hemoglobin (such as pregnancy or certain rare diseases).
Nitrate in drinking water starts affecting the health of the general populace at
levels in the range of 100 to 200 mg/l nitrate-N, but the effect on any given
person depends on many factors, including other sources of nitrate and nitrite
in the diet. Some of the nitrate consumed can be converted in the body to
nitrite, which under appropriate circumstances can combine with amines (portions
of protein molecules often found in foods, medications, cigarette smoke,
decaying plants, soil, and sometimes water) to form nitrosamines, well-
documented cancer-causing substances. So far, the only studies linking nitrate
in drinking water with cancer have involved nitrate levels that are quite high
(at or above 100-200 mg/l nitrate-N).
What Are the Most Common Sources of Nitrate in People's Diets?
Water with nitrate levels below the health standard usually supplies an almost
negligible percentage of an adult's nitrate intake. Eighty to 90 percent of the
nitrate most people consume comes from vegetables, but this is unlikely to cause
health problems because very little of the nitrate in vegetables is converted to
nitrite. Meat products account for less than 10 percent of nitrate in the diet,
but 60 to 90 percent of the nitrite consumed. This is primarily because of
sodium nitrite added to foods such as hot dogs, bacon, or ham. Fruits, grains,
and dairy products contribute almost no nitrate or nitrite to people's diets.
How are Safety Standards for Drinking Water Set?
Congress passed the federal Safe Drinking Water Act in 1974. The U S.
Environmental Protection Agency was given responsibility for setting drinking
water standards for all the states, and each state became responsible for
enforcing these standards. In New York State, the Department of Health regulates
all public water supplies serving 25 or more people.
Because potential health risks are often unknown or hard to predict, many
drinking water standards are set at some fraction of the level of "no-observed
adverse-health effects." In general, the greater the uncertainty about potential
health effects, the greater the margin of safety built into the standard.
In the case of nitrate, there may not be a large safety factor. A 1977 report by
the National Academy of Science concluded that "available evidence on the
occurrence of methemoglobinemia in infants tends to confirm a value near 10 mg/l
nitrate as nitrogen as a maximum no-observed adverse-health-effect level, but
there is little margin of safety in this value."
Where Can I Get My Water Tested for Nitrate?
Public water supplies in New York State are tested for nitrate at least annually
if the source is surface water and at least once every 3 years if the source is
groundwater. If nitrate levels are found at or near the health standard, then
tests are run more frequently, and potential sources of the nitrate are
investigated. You should be able to get the results of tests for a public water
supply from your municipal water department, or your county or regional office
of the NYS Department of Health.
If you use a private water supply, there are no routine tests done for nitrate.
You can get your water tested for nitrate at a private laboratory for about 10
to 15 dollars. To locate a NYS-certified laboratory in your area that tests for
nitrate, you can check with your county Cooperative Extension office or your
county or regional health department, or you can look in the Yellow Pages of the
phone book under "Laboratories-testing."
Once you have located a laboratory, be sure to ask how to collect, store, and
ship the sample. In most cases, the sample should be chilled or frozen and
possibly fixed with sulfuric acid to prevent bacteria from changing its original
How Can I Lower the Nitrate Level in My Current Water Supply?
The best solution is to find an alternative water supply for drinking and
cooking water purposes. Another possibility is to try to remove or reduce the
source of nitrate contamination, although reduction of nitrate concentrations in
your well is unlikely to be immediate. Your county Cooperative Extension office
and local or regional Department of Health may be able to assist you in locating
and cleaning up contaminant sources.
There are no simple ways to remove nitrate from water in the home. Because
nitrate does not evaporate the way chlorine does, boiling, freezing, or letting
water stand does not reduce the nitrate level. In fact, boiling water for more
than 10 minutes can make the nitrate more concentrated. Boiling water in an
aluminum pan may also convert nitrate to nitrite.
Home water-treatment units are generally a limited option. A properly operating
distillation system will remove nitrate, but is quite expensive to install and
operate and must be adjusted properly. Reverse-osmosis units are another option,
but also are expensive to install and operate. Anion-exchange units are
relatively inexpensive, but have the serious drawback of being effective for
only a short period of time (a matter of months, depending on the contents of
the water) before the unit becomes saturated and needs to be recharged. For any
treatment unit, frequent water testing is necessary to determine whether the
system is still working effectively.
Where Can I Get Low-Nitrate Water?
If your private or public water supply has elevated nitrate levels, then
purchasing bottled water is one of your best alternatives. Even in bottled
water, nitrate levels can vary considerably. Some states require bottled water
companies to have their water tested for nitrate annually. As long as the
results are below the state standard, the companies don't have to report the
actual levels to the Department of Health, but they should be willing to give
exact test results to consumers. In general, distilled or mineral-reduced water
is more likely to have low-nitrate levels than spring or mineral water.
Municipal water supplies are another potential source of low nitrate water. City
water supplies often come from large lakes or reservoirs where any source of
nitrate is likely to be diluted by the large quantity of water.
Hauling your own water from springs, lakes, or streams can be risky, both
because of the unknown levels of nitrate and because of the possible presence of
other contaminants, especially bacteria. Private wells also present the risk of
unknown nitrate levels, but are more likely to have been tested for bacterial
Risks also are associated with collecting rainwater. Rooftop cisterns often
contain lead solder, which can be dissolved by rainwater. Also, rain collected
off a roof can contain asbestos or other contaminants from the roofing material.
Alternative water supplies are only as good as their source, their collection
method, and their storage. Before using any source of water, find out exactly
what the levels of nitrate and bacteria are in that supply. Bacterial
contamination is a double problem: it may be responsible for the reduction of
nitrate to nitrite; but more importantly, the bacteria themselves can cause
For Further Reading
Feig, Stephen. 1981. Methemoglobinemia. In Hematology of infancy and childhood,
ed. D.G. Nathan and F.A. Oski. W.B. Saunders Co., Philadelphia.
National Academy of Sciences, Committee for Scientific and Technical Assessments
of Environmental Pollutants. 1978. Nitrates: An environmental assessment.
National Academy of Sciences, Committee on Nitrite and Alternative Curing Agents
in Food. 1981 . The health effects of nitrate, nitrite, and N-nitroso compounds.
National Academy of Sciences, Safe Drinking Water Committee. 1977. Drinking
water and health. Washington, D.C.
Russell, C.S., ed. 1978. Safe drinking water: Current and future problems.
Resources for the Future, Inc., Washington, D.C.
Shearer, L.A., J.R. Goldsmith, C. Young, et al. 1972. Methemoglobin levels in
infants, in an area with high nitrate water supply. Amer. J. of Public Health,
Shuval, H.I., and N. Gruener. 1972. Epidemiological and toxicological aspects of
nitrates and nitrites in the environment. Amer. J. of Public Health, 62:1045-51.
Acknowledgments: Illustrations were drawn by Donna Curtin, and Mary Jane Porter
served as production assistant. Funding was provided by the New York Farmers'
Fund. Many individuals reviewed the initial drafts, including Cornell University
faculty members and northeastern Cooperative Extension agents.