Nitrates in Well Water: Safe Levels and How to Remove Them

The EPA’s maximum contaminant level for nitrate is 10 mg/L measured as nitrogen. The limit exists to protect babies under six months, whose blood can lose its ability to carry oxygen (methemoglobinemia, or “blue baby syndrome”). If your well is over 10 mg/L, use bottled water for infant formula and drinking, do not boil the water, and treat it with reverse osmosis, anion exchange or distillation after fixing the source if you can.

Nitrate has no taste, color or smell. A lab test is the only way to know your level, and the CDC says every well owner should test for it at least once a year.

What your nitrate number means

First check the units on the lab report. Nitrate can be reported as nitrogen (nitrate-N, NO3-N) or as nitrate (NO3). The same water gives a number about 4.4 times higher when reported as nitrate: NSF’s test protocol equates 30 mg/L as N with 132 mg/L as NO3. The EPA limit of 10 mg/L as N is therefore roughly 44 mg/L as NO3. A report showing “25 mg/L nitrate” may be under the limit or well over it, depending on which basis the lab used.

With the number in mg/L as N (1 mg/L equals 1 ppm), Oregon State University Extension groups results like this:

The Minnesota Department of Health (MDH) adds two reference points: natural nitrate levels are usually under 3 mg/L, and levels above 3 mg/L suggest human sources even when they are below the EPA limit. Levels above 10 mg/L usually come from runoff, leaks or wastewater.

Nitrite, a related compound, has its own EPA limit of 1 mg/L as nitrogen. Many labs report the two together.

Who is at risk

MDH identifies bottle-fed babies under six months as the highest-risk group, and notes that the symptoms, such as bluish lips or skin, can be hard to spot. The EPA states that infants under six months who drink water with high nitrate can become seriously ill and die. MDH also lists people with glucose-6-phosphate-dehydrogenase deficiency and some other metabolic conditions as higher risk.

For pregnancy, Oregon State Extension says nitrate may increase the risk of birth defects, low birth weight, preterm birth and miscarriage. MDH describes possible links below the standard, including thyroid problems and adverse pregnancy outcomes, as areas needing more research. MDH recommends a nitrate test before bringing a newborn home.

Adults can generally shower, wash dishes and do laundry with high-nitrate water, according to Oregon State Extension, because nitrate is not readily absorbed through skin. Supervise children so they do not swallow bath water.

Where nitrate comes from

The EPA and MDH name the same sources: fertilizer, septic systems, manure and other animal waste, feedlots and sewage. MDH lists the wells most at risk:

• Shallow wells, and wells in sand, karst or fractured rock
• Dug wells without watertight casings
• Wells with damaged or leaking casings or fittings
• Older wells, and wells close to septic systems or farmland

Because the same routes carry bacteria, Oregon State Extension recommends testing for coliform whenever nitrate is high. See our page on coliform in well water.

What does not work

• Boiling. It makes nitrate more concentrated. MDH and Oregon State Extension both warn against it.
• Activated carbon pitchers and refrigerator filters. They do not remove nitrate.
• Chlorine and other disinfectants. Nitrate is a chemical, not a germ.
• A standard water softener. Softener resin targets hardness minerals, not nitrate. Oregon State lists only reverse osmosis, anion exchange and distillation as nitrate treatments.

Treatment options

Oregon State Extension compared the three methods, with cost ranges built from 2017 quotes and 2018 research (low end assumes owner installation, high end professional installation):

Reverse osmosis

An RO membrane holds back nitrate along with many other dissolved contaminants, and for drinking and cooking water a single under-sink unit is usually enough. Look for certification to NSF/ANSI 58 with a nitrate/nitrite reduction claim; the standard’s long-standing test challenges units at 30 mg/L as N. NSF later added a separate high-nitrate claim, and units that need a booster pump to reach it must say so in their literature. Low well pressure reduces RO output, so check the unit’s minimum inlet pressure against your pressure switch setting. Our reverse osmosis systems for well water roundup compares units suited to well water; confirm the nitrate claim on any unit you shortlist.

Anion exchange

A whole-house tank of nitrate-selective resin swaps nitrate for chloride and regenerates with salt, much like a softener. It treats every tap but adds chloride to the water, which Oregon State Extension notes can make water more corrosive to copper or lead plumbing. If regeneration is skipped, the resin can release nitrate back in a concentrated slug, so this method suits owners who will keep up with salt and service.

Distillation

A countertop distiller boils water and condenses the steam, leaving nitrate behind. Oregon State Extension notes it also kills bacteria and viruses, so it keeps working during a boil-water advisory. It is slow, so it only makes sense for drinking and cooking water.

Oregon State Extension recommends testing treated water for nitrate every year to confirm the system still works. MDH adds that babies under six months should not drink home-treated water and that bottled water may be safer for them.

Fix the source first

MDH advises having a licensed well contractor inspect the well and identify nitrate sources before relying on treatment. Oregon State Extension’s prevention list includes keeping manure piles and septic systems at least 50 feet from the well, keeping the wellhead 12 inches above ground with a sanitary seal, finding and sealing unused wells on the property, installing backflow preventers on outdoor spigots, and pumping the septic tank on schedule (every 3 to 4 years for a typical four-person household).

How often to retest

Test at least once a year, per the CDC. Nitrate rises and falls with the seasons, so Oregon State Extension suggests sampling in both spring and fall to catch trends. Test again before a baby arrives, after a pregnancy begins, after new fertilizer or septic work nearby, and after installing treatment. Our well water testing guide covers certified labs and sampling, and our well water test kit comparison covers mail-in lab kits.