Nitrates in Well Water: Health Risks, Safe Levels & How to Remove Them

Nitrate is a form of nitrogen that soaks down into well water from fertilizer, manure and septic systems. You cannot see it, smell it or taste it, so the only way to know your number is a lab test. The EPA limit is 10 mg/L measured as nitrogen, which is how the lab report from our well test prints it: "Nitrate (as N)". At 10 or more, EPA says to switch to another source of drinking water, and the water is dangerous for a baby under 6 months. Check the unit on your report, because 10 as nitrogen is about 44 as nitrate.

Most of the well tests my customers get back come in under the limit. Of 222 with a nitrate result since August, 4 came back at 10 or more. But 52 came back at 3 or more, the level Minnesota's health department says points to a human source like fertilizer, manure or a septic system.

What your nitrate number means

Under 10 mg/L as nitrogen is under the EPA limit. Here is what each range means, and how the well tests my customers got back since August came out.

The EPA limit for nitrate and nitrite added together is also 10 as nitrogen. These are EPA's limits as it lists them in September 2026. EPA says to test a private well every year for nitrate, bacteria, total dissolved solids and pH, and the complete well water test covers all four from one sample.

Check the unit on your report

A nitrate number means nothing until you know its unit. The EPA limit is written as nitrogen, and the lab behind our well test prints nitrate and nitrite that way, in ppm, which is the same as mg/L. A report that counts the whole nitrate molecule instead ("as NO3") reads about 4.4 times higher for the same water, so on that scale the limit is about 44 (ATSDR).

A caller in California shows why this matters. A dealer's salesman had told him his well tested 77. He figured that was nitrate as NO3, which is about 17 as nitrogen, and ordered a nitrate system from us. I told him to get a water test to back up the number. The lab's answer was 7.7 as nitrate, which is 1.7 as nitrogen. "Your water's fine," they told him, and he did not need the system at all. As I told him, "That's why we tell everybody we don't sell anything until people give us a water test or have some kind of results."

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Who is most at risk from nitrate

Babies under 6 months are most at risk. EPA says infants that age who drink water over the limit "could become seriously ill and, if untreated, may die." The illness is methemoglobinemia, or blue baby syndrome. Nitrate turns into nitrite in the body, and nitrite changes the blood so it cannot carry oxygen. Minnesota's health department says it can turn the lips and skin bluish, but it may be hard to see in a baby.

For a bottle-fed baby, the main source is the well water used to mix formula, ATSDR says, "especially when the water is boiled prior to use." Minnesota's health department goes further: even with treatment in the house, it recommends that babies under 6 months not drink the well water, in case the treatment fails.

ATSDR, the federal agency for toxic substances, gives three reasons babies are hit hardest:

• A baby's stomach is less acidic, which lets bacteria there turn more nitrate into nitrite.
• A baby's blood (fetal hemoglobin) is damaged by nitrite more easily than an adult's.
• The enzyme that repairs that damage works at about half the adult rate.

Pregnancy matters too. Wisconsin's health department says nitrate can raise the risk of neural tube defects, which form very early in pregnancy, and tells anyone who is or may become pregnant to use a different water source when nitrate is 10 or more. ATSDR's 2013 case study says the research on pregnancy is not conclusive.

Minnesota's health department also points to newer research linking long-term nitrate, even under the limit, to thyroid problems, pregnancy problems and colorectal cancer, and says more research is needed to confirm it. When someone calls me with nitrate over 10, I tell them I don't recommend drinking the water or giving it to children or pets.

What to do when nitrate hits 10

1. Drink bottled water. Use it for drinking, cooking, and mixing formula and baby cereal (EPA, Nebraska Extension).
2. Do not boil the water. Boiling does not remove nitrate. Some of the water boils off and the nitrate stays, so the level goes up (EPA). As I tell people, boiling fixes a bacteria problem if you boil it long enough, not a nitrate problem.
3. Keep showering. Bathing, showering and washing dishes are fine (EPA, Wisconsin health department).
4. Retest to confirm the number. Wisconsin's health department says to retest your well to verify the result. The complete well water test reports nitrate, nitrite and hardness from one sample, and hardness matters because a whole-house nitrate filter needs a softener ahead of it when the water is hard. How to Test for Nitrates in Well Water covers which test to use and when.
5. Pick a treatment. See what removes nitrate.
6. Test the treated water. After treatment goes in, test the water it puts out to make sure it is working (Minnesota Department of Health).

What removes nitrate from well water

A whole-house nitrate filter removes nitrate at every faucet. An under-sink reverse osmosis system lowers it at one faucet, the kitchen sink. A distiller also removes nitrate (CDC). Boiling, a standard water softener, carbon filters (Brita-style pitchers included) and UV lights do not remove it (EPA, Nebraska Extension, CDC).

A whole-house nitrate filter looks just like a water softener. The difference is the resin inside, which is made to take out nitrate. It has its own salt tank and regenerates on its own, so the upkeep is keeping salt in the salt tank, the same as a softener.

Every nitrate filter we sell uses a nitrate-selective resin. Ordinary anion resin can dump nitrate back into the water, and the selective kind avoids that (Water Quality Association).

The two systems do not take out the same amount. A caller whose strips read up to 20 asked me about it, and I told him, "a reverse osmosis might give you 50 percent reduction, maybe 70 under optimal conditions, whereas the whole house filter will give you 100 percent reduction." At 20, a 50 percent reduction still leaves 10, right at the limit. How much an RO takes out depends on water temperature and pressure, which is why the numbers vary: Penn State Extension reports 83 to 92 percent, and I tell callers about 50, up to 70.

If your water is hard, I tell people to put the softener first and the nitrate filter after it, so the nitrate resin works at its best. If the pH is low too, the order I give callers is "a neutralizer, a water softener, and then a nitrate filter." The system goes in where the water comes into the house, to catch all the water "before it branches off." Every tank ships empty, with the resin in separate bags that are loaded into the tank at install, and drain tubing is not included. We recommend a licensed plumber, and I support your plumber by phone at 800-460-5810.

In this video I answer the questions people ask me most about nitrate: boiling, softeners, carbon, reverse osmosis and the whole-house filter.

The rest of the treatment answers each have their own guide:

• Best Nitrate Filter for Well Water covers which model and size fits your house.
• How to Remove Nitrates from Well Water covers how the system works and the order the tanks go in.
• Nitrate Filter Cost & Maintenance covers what it costs to run and how long the resin lasts.

Where nitrate in well water comes from

Nitrate comes from fertilizer, manure and septic systems. It is most common in shallow wells in farm country. When people ask me where it comes from, I usually tell them it's farmers using fertilizers made from animal waste. EPA also lists leaking septic tanks and sewage, and small amounts from natural deposits.

USGS found nitrate over the limit in about 7 percent of domestic wells nationwide, and in more than 20 percent of shallow wells in farm areas (samples from 1992 to 2004). Minnesota's health department lists the wells most likely to pick it up: shallow wells, wells in sand, karst or fractured rock, dug wells whose casings are not watertight, and wells with damaged casings.

The level also moves with the seasons. ATSDR says wells can test higher during spring melt or drought, so one low test near fields does not settle it. Test every year.

Frequently asked questions