Nitrate in Tap Water: Infant Risks, Private Wells, and What Removes It

Nitrate is a form of nitrogen that gets into drinking water mainly from fertilizer, septic systems and animal waste. EPA’s enforceable limit is 10 mg/L measured as nitrogen, set to protect babies under six months, who can become seriously ill from “blue baby syndrome” if their formula is made with high-nitrate water. Public water systems must test for it and notify customers within 24 hours of a violation. Private wells, especially shallow wells in farm country, carry the most risk because nobody tests them unless the owner does. Boiling does not remove nitrate; it concentrates it. Reverse osmosis, ion exchange and distillation can remove it.

What the limit means

EPA sets two limits for this family of chemicals:

Nitrate: 10 mg/L as nitrogen (both the enforceable limit and the health goal)
Nitrite: 1 mg/L as nitrogen

“As nitrogen” matters. Labs and reports sometimes express nitrate as the whole nitrate ion instead, which makes the number about 4.4 times larger. WHO’s guideline, for example, is 50 mg/L as nitrate, which WHO notes is about 11 mg/L as nitrogen, very close to the US limit. If your lab report shows a number in the 40s, check the units before drawing conclusions. Minnesota’s health department adds that natural processes usually keep nitrate below 3 mg/L, so higher readings usually point to a human source.

Why babies are most at risk

EPA’s standard is built around infants. In its words, babies under six months who drink water with nitrate above the limit could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome.

The medical name is methemoglobinemia. Too much nitrate interferes with the blood’s ability to carry oxygen, which can give a baby’s skin a bluish tint. Minnesota’s health department says bottle-fed babies under six months are at the highest risk, because formula mixed with tap water can be most or all of what they take in. WHO notes the risk is higher when an infant also has a gut infection caused by germs in the water.

Minnesota’s guidance also flags longer-term questions: research suggests possible links between long-term exposure below the standard and thyroid problems, adverse pregnancy outcomes and some cancers, particularly colorectal. The department notes more research is needed. If you’re pregnant or have a health condition and your water has elevated nitrate, ask your doctor.

Where nitrate comes from

EPA lists the main sources as runoff from fertilizer use, leaking septic tanks and sewage, and erosion of natural deposits. Minnesota adds animal feedlots, landfills and urban drainage.

Nitrate dissolves easily and moves with water, so it leaches down through soil into groundwater. That’s why it’s mostly a groundwater problem, and why shallow wells near cropland or septic fields are the most exposed.

Private wells carry the most risk

USGS’s national assessment of nutrients in groundwater (Circular 1350, covering 1992–2004) sampled 2,388 domestic wells and found nitrate above the 10 mg/L limit in about 7% of domestic wells overall and in more than 20% of domestic wells in agricultural areas. Domestic wells tend to be shallower than public supply wells, which makes them more vulnerable.

Because the Safe Drinking Water Act doesn’t cover private wells, the owner is the only one testing. Both CDC and Minnesota’s health department recommend testing a private well for nitrate every year. Minnesota adds:

Test before bringing a newborn home.
A result above 1 mg/L is a reason to test further, because pesticides may also be present.
Use an accredited lab.

Our well water testing guide covers the full annual testing panel.

Public water systems

If you’re on city water, nitrate is regulated and tested. Systems test at least once a year, and nitrate appears in the detected contaminants table of your annual Consumer Confidence Report.

A nitrate violation is treated as urgent. Under EPA’s Public Notification Rule, exceeding the nitrate or nitrite limit is a Tier 1 violation: the system must notify everyone it serves within 24 hours of learning about it.

In TapWaterSafety.org’s dataset of 1,000 public water systems (EPA ECHO compliance records, checked October 7, 2026; last 12 quarters), none had a nitrate maximum contaminant level violation. Forty-five systems had a Nitrate Rule monitoring or reporting violation, meaning a required sample or report was missed or late, and 42 of those were still listed as open. A monitoring violation is a paperwork and testing gap, not a finding that nitrate was too high, though it does mean the system’s results for that period weren’t confirmed on schedule. Utilities may have resolved issues since; check your system’s EPA report or latest Consumer Confidence Report. You can look up your utility to see its full record.

What to do if your nitrate is high

Don’t boil it. Minnesota’s health department is clear: boiling concentrates nitrate because water evaporates and the nitrate stays behind.

Use another water source for babies. If nitrate is above 10 mg/L, use a safe alternative such as bottled water, especially for formula for babies under six months. Minnesota recommends bottled water for infants under six months even if you have a treatment system, in case the system stops working. See our guide on tap water for baby formula.

For wells, look for the source first. Minnesota recommends reducing nitrate sources around the well and having a licensed well contractor make sure the well is built and working properly before relying on treatment. A damaged or poorly sealed well can let contamination in more easily.

Retest. Nitrate levels can change over time. Keep your records so you can see trends.

Filters that remove nitrate

EPA lists three home treatment methods for nitrate: distillation, reverse osmosis or ion exchange.

Reverse osmosis (RO). RO pushes water through a membrane that holds back nitrate along with many other dissolved substances. Look for certification to NSF/ANSI 58 with a nitrate/nitrite reduction claim; NSF notes that only complete systems can carry contaminant reduction claims, and claims are product-specific, so check the listing. RO wastes some water. Our reverse osmosis vs. carbon filters guide covers the trade-offs.

Ion exchange (anion exchange). This works like a water softener but with a resin that swaps nitrate for chloride. Washington State’s health department notes that ion exchange produces a waste brine that is very high in salt and nitrate, so disposal matters.

Distillation. Boils water and condenses the steam, leaving nitrate behind.

What doesn’t work: Washington’s health department notes that nitrate’s chemistry makes it difficult to remove with conventional filtration or activated carbon. A standard carbon pitcher or refrigerator filter is not a nitrate solution. Check a product’s certification listing before buying.

Because nitrate is an acute risk for infants, Washington’s guidance also stresses that an undetected treatment failure can be an immediate health risk. Replace membranes and cartridges on schedule and test treated water periodically.

Bottom line

For most people on city water, nitrate is well controlled, tested yearly and subject to 24-hour public notice if the limit is exceeded. The real risk is private wells, especially shallow ones near farms or septic systems, and the people most affected are babies under six months. Test well water every year and before a baby arrives, never boil high-nitrate water, use bottled water for infant formula if your level is high, and choose an NSF/ANSI 58 certified RO system or ion exchange if you need treatment.