Nitrates in Water

The short answer

Nitrate is a compound that occurs naturally and also comes from fertilizer, septic systems and animal waste. The Minnesota Department of Health says you cannot taste, smell or see nitrate in water, and that consuming too much of it can be harmful, especially for babies.

Two numbers frame most nitrate results:

• The nitrate limit is 10 mg/L^[1], measured as nitrogen. That is EPA's maximum contaminant level (MCL) for public water systems. EPA's health goal is the same value, 10 mg/L^[1].
• The nitrite limit is 1 mg/L^[1], also measured as nitrogen. Nitrite is a related compound with its own, lower limit.

MDH notes that public water systems test for nitrate at least once a year. A private well is tested only when its owner orders a test, and CDC says all well owners should test for nitrates at least once every year. Our nitrate water test guide explains how to take the sample, and our water testing cost guide shows verified lab prices. If the lab doesn't detect nitrate, no treatment is needed based on that result.

Nitrate levels and what to do

The table below lines up the federal nitrate benchmarks with what each kind of result means for your household. The values come from our versioned benchmark data, which records EPA's figures and the date we last checked them.

How the nitrate limit works

For nitrate, the legal limit and the health goal are the same number. The Minnesota Department of Health explains that, based on the data available now, the federal standard protects infants against methemoglobinemia, a condition that affects how blood carries oxygen. Infants are the most sensitive group for the known health effects.

So a result at or above the MCL matters most for a household with a baby. Below it, the result is under the federal limit, but MDH notes that research on long-term effects below the current standard is still going on, as the health section below explains.

Check the units on your report

Both the nitrate and nitrite limits are written as nitrogen. Look for "as N" or "as nitrogen" next to your result. If your report gives nitrate in another form, ask the lab to give you the result as nitrogen before you compare it with the limit. A report that lists nitrate and nitrite separately can be compared with each limit in turn. Our guide on how to read your lab report explains the other units and terms you will see on it.

Health effects of nitrate in drinking water

In the notice EPA requires water systems to send when nitrate is above the standard, EPA calls nitrate an acute contaminant. Its drinking water regulations say infants below six months who drink water containing nitrate above the MCL could become seriously ill and, if untreated, may die. The symptoms EPA lists include shortness of breath and blue-baby syndrome. EPA gives the same warning for nitrite above its own MCL.

Why babies. The Minnesota Department of Health explains that consuming too much nitrate can affect how blood carries oxygen and cause methemoglobinemia, also known as blue baby syndrome. Bottle-fed babies under six months old are at the highest risk. The U.S. Geological Survey notes that infants lack the enzyme needed to correct the condition. MDH says it can turn the lips and skin a bluish color but may be difficult to detect in infants, and that symptoms often resolve once the nitrate source is removed. People with glucose-6-phosphate dehydrogenase deficiency or other metabolic conditions may also be at higher risk.

Long-term research. MDH reports newer research on long-term exposure to nitrate in drinking water at levels below the current standard. The possible effects it names include thyroid problems, adverse pregnancy outcomes and cancers, particularly colorectal. MDH says further research is needed to confirm these findings, and that it will update its guidance when the data are adequate.

Swallowing is the route. EPA says nitrate is only a concern for ingestion, meaning eating and drinking. It is not absorbed through your skin, so showering and bathing are not how nitrate in water reaches you.

A water test measures nitrate in your water, not in anyone's body. If a baby in your home has been drinking water above the MCL, or you have other health concerns, talk to a health professional and bring your lab report.

Nitrates in well water: where they come from

Nitrate usually reaches a well from the land around it. EPA lists the sources of nitrate in drinking water as runoff from fertilizer use, leaking from septic tanks and sewage, and erosion of natural deposits. CDC's list for well water is longer: animal waste, septic systems, wastewater, flooded sewers, polluted storm water runoff, fertilizers, runoff from farms and decaying plants. CDC adds that whether a well has nitrates also depends on the geology around it.

Natural and human-made. The Minnesota Department of Health notes that nitrate comes from natural processes, such as plant decay and lightning, and is found in some foods. It is also in many fertilizers used on yards, gardens, golf courses and crops. MDH says natural processes usually cause only low levels in drinking water, and that high levels can come from fertilized soil, wastewater, landfills, animal feedlots, septic systems or urban drainage.

Which wells are most exposed. MDH names the wells most vulnerable to nitrate: wells in sand, karst and fractured rock aquifers, and wells with damaged or leaking casings or fittings. The risk is higher for older wells, built before 1974^[6], and for wells near septic systems or in areas with agricultural activity.

How often wells exceed the limit. The U.S. Geological Survey sampled domestic wells across the country and found nitrate above the EPA MCL in 4.4 percent^[5] of them, most often in agricultural areas. In a separate look at wells in areas of intense agricultural land use, nitrate was above the MCL in nearly 25 percent^[5] of about 400^[5] wells. USGS found the highest concentrations in the upper Midwest, the Great Plains and California's Central Valley. Nitrate was the only contaminant from mainly human-made sources that USGS found above a health benchmark in more than 1 percent^[5] of wells.

A sign to look further. CDC says that if your water has high levels of nitrates, other harmful chemicals or germs might also be in it. MDH gives pesticides as an example. Our well water testing guide covers the full yearly well check, and you can build a test plan that fits your well and household.

When to retest for nitrate

CDC and the Minnesota Department of Health both advise testing a well for nitrate every year. Retest sooner in these situations:

• To confirm a high result. If nitrate was at or above the MCL, retest with a state-certified lab before you decide on treatment. MDH's first step for a result above the MCL, drinking water from another source, applies while you wait.
• Before a baby arrives. MDH says that if you have recently had a baby, test your well before bringing your baby home. CDC also names the times when you or someone you live with becomes pregnant, or a child starts living with you.
• After problems near your well. CDC lists flooding, land disturbances and nearby waste disposal sites.
• After work on the well. CDC lists replacing or repairing any part of your well system.
• When your water changes. CDC lists a change in your water's taste, color or smell.
• After you install treatment. MDH says to test the treated water after installing a unit to make sure it works, and to keep up the maker's maintenance.

MDH also notes that nitrate well below the EPA standard, but above the low levels natural processes usually cause, can suggest that human-made sources have reached the water, and that the level could rise over time. That is a reason to keep up the yearly test rather than stop after one clear result.

How to lower nitrate in your water

Start with a confirmed result from a state-certified lab. What you do next depends on what it shows, and "no treatment needed" is a real outcome.

If nitrate was not detected, or is below the MCL, no treatment is needed based on the federal limit. Keep testing every year.

If a confirmed result is above the MCL, the Minnesota Department of Health lays out these steps, in this order:

1. Use another source of drinking water, such as bottled water, until you fix the problem. MDH says this is especially important if babies under six months drink formula made with the water.
2. Don't boil the water. EPA says boiling will not reduce nitrate. It makes the level worse, because some of the water evaporates but the nitrate does not.
3. Have a licensed well contractor inspect the well for damage.
4. Find and remove nitrate sources on your property, such as fertilizer, septic systems and animal waste near the well.
5. Then consider home treatment. MDH says treatment may be an option once you have dealt with the sources and a licensed well contractor has found the well is working properly.

In summary, MDH's home water treatment guide lists reverse osmosis and distillation among the units designed to remove nitrate, along with anion exchange, where the resin is certified for it. MDH advises choosing a unit certified by NSF, UL or the Water Quality Association for the contaminant you want removed. Because nitrate matters only when swallowed, EPA notes that many people install nitrate treatment just at the kitchen faucet they use for drinking and cooking.

MDH adds a caution for babies: it recommends that no baby under six months drink the treated water, and says bottled water may be a safer choice for them in case the treatment stops working. Retest the treated water with a certified lab after installation, and keep testing every year.