Nitrate in Well Water: Read Your Result and Choose Treatment

If your nitrate result is at or above 10 mg/L as nitrogen, or you suspect harmful contamination, use known-safe water for the household’s drinking, cooking, and infant formula now. Bottled water or another verified safe supply can cover those needs while you contact your health department. Do not wait for a repeat sample or a treatment installation to change drinking water sources. CDC guidance on contaminated wells

Infants younger than six months are especially vulnerable: nitrate exposure can cause methemoglobinemia, which impairs the blood’s ability to carry oxygen. Formula made with contaminated water is a particular concern. High nitrate exposure can affect other household members too, so precautions should not stop with babies. Seek urgent medical care for an infant with breathing difficulty or bluish skin. EPA nitrate health information; Wisconsin health guidance

Read the reporting basis before comparing numbers

The words after the number matter. A laboratory can report nitrate using the mass of its nitrogen component or the mass of the entire nitrate ion. These produce different numbers for the same water.

Report wording	Comparison benchmark	How to read it
Nitrate as N, nitrate-N, or NO3-N	10 mg/L as nitrogen	Compare directly with the nitrate benchmark.
Nitrate as NO3 or nitrate ion	Approximately 44.3 mg/L as NO3	This is the converted equivalent of 10 mg/L as N.
Nitrite as N or NO2-N	1 mg/L as nitrogen	Nitrite is a separate analyte with a separate benchmark.
“Nitrate” without a reporting basis, or nitrate plus nitrite	Ask the laboratory	Do not assume the reporting basis or treat a combined result as nitrate alone.

EPA sets public-system maximum contaminant levels of 10 mg/L for nitrate as nitrogen and 1 mg/L for nitrite as nitrogen. These federal standards apply to public water systems; they serve as comparison benchmarks for private wells, not federal private-well requirements. EPA drinking-water standards; CDC private-well guidance

Where 44.3—and the rounded 45—come from

The conversion is a molecular-mass calculation. NO3 contains one nitrogen atom and three oxygen atoms. Using approximate atomic masses of 14 for nitrogen and 16 for oxygen:

• Nitrate ion mass: 14 + (3 × 16) = 62.
• Convert nitrate as N to nitrate as NO3: multiply by 62/14, approximately 4.43.
• Thus, 10 mg/L as N × 62/14 = approximately 44.3 mg/L as NO3.
• Convert back by multiplying nitrate as NO3 by 14/62.

The 45 mg/L figure used as a rounded guide value is not the precise conversion. For example, a hypothetical result of 44.5 mg/L as NO3 converts to approximately 10.05 mg/L as N; comparing it only with 45 could obscure an exceedance. Ask the lab to confirm both the reporting basis and its interpretation, especially near the benchmark. The calculation above converts EPA’s nitrogen-based value; EPA’s cited table itself reports the standard as nitrogen.

Turn the result into a decision

At or above the benchmark, or contamination suspected: keep using known-safe drinking and cooking water. Contact public health, confirm units with the laboratory, and arrange repeat testing as directed. Wisconsin’s private-well guidance calls for action at 10 mg/L nitrate-nitrogen or above. Wisconsin nitrate guidance

Below the benchmark: keep the dated report and compare it with earlier results on the same reporting basis. A rising result or one close to the benchmark warrants discussion about earlier retesting, particularly when someone is pregnant or an infant will use the water. Nitrate can vary seasonally. A low nitrate result says nothing about contaminants the lab did not test. Oregon State University nitrate guide

Unclear report: ask, “Is this nitrate alone, nitrite alone, or a combined measurement, and is it reported as nitrogen?” Do not resolve uncertainty by assuming the more favorable interpretation.

Use a drinking-water laboratory whose state certification covers the requested nitrate analysis. Confirm nitrite coverage if ordering that test too. Our well water testing guide explains how to organize the testing request; state resources can help you find local contacts. For kit vs lab vs strip choices, see how to pick the right test kit. CDC laboratory guidance

Boiling does not remove nitrate

Boiling leaves nitrate behind while water evaporates, potentially increasing its concentration. Ordinary activated-carbon pitcher or refrigerator filters do not remove nitrate, and chlorine disinfection does not remove it either. Boiling for germs is a different process from treating a chemical contaminant. Oregon State University treatment guidance

A nitrate result alone does not call for a blanket bathing ban. Wisconsin allows bathing with nitrate-contaminated well water, and Oregon State explains that nitrate is not readily absorbed through skin. Avoid swallowing bathwater and supervise children. This advice does not establish that flooded water or water containing fuel or unidentified chemicals is suitable for bathing; those situations need separate public-health instructions. Wisconsin nitrate guidance; Oregon State University nitrate guide; EPA flood precautions

Choose treatment with verified nitrate performance

Reverse osmosis, distillation, and anion exchange can reduce nitrate. No treatment category guarantees that every model will work with your incoming concentration and water chemistry. Verify the exact model’s nitrate-reduction claim and applicable certification listing before purchase. Oregon State University treatment options

Treatment	What to establish before buying
Reverse osmosis	Verify nitrate performance, any pretreatment needs, treated-water output, wastewater production, and maintenance requirements.
Distillation	Verify nitrate performance and whether output meets drinking and cooking needs. Account for electricity and cleaning. Distillation collects condensed steam; drinking water left in a boiling pot does not accomplish this.
Nitrate-selective anion exchange	Specify nitrate treatment. An ordinary hardness softener is not a substitute. Have a treatment professional assess sizing, water chemistry, regeneration, and waste handling.

Anion exchange needs careful maintenance: Oregon State warns that improperly maintained equipment can release high contaminant concentrations back into the water and may affect corrosivity. Ask for a written operating and monitoring plan. For the separate hardness problem, see hard well water. Oregon State University treatment guidance

A system serving one faucet requires everyone to use that outlet for drinking and cooking. Whole-house treatment serves more outlets but introduces different capacity and wastewater considerations. Include ice and formula preparation when deciding how much treated water you need.

Before relying on treatment, arrange a laboratory test of the treated water to confirm that it worked. Ask the lab to identify suitable untreated and treated sampling locations, and follow its collection and delivery instructions. Keep using the alternative supply until treatment results and public-health advice support resuming use. A successful nitrate test verifies nitrate performance only. CDC treatment guidance

Keep testing and investigate the source

CDC and EPA recommend testing private wells at least annually for nitrate, total coliform bacteria, total dissolved solids, and pH. Test sooner after flooding, well repairs, nearby contamination concerns, or changes in water quality. Pregnancy or a child joining the household also warrants testing. For elevated nitrate or installed treatment, ask about additional monitoring; continue annual nitrate testing of treated water. CDC testing schedule; EPA well protection; Oregon State University monitoring guidance

Fertilizer, manure, septic wastewater, and natural sources can contribute nitrate. A result cannot identify which source caused it. Ask public health about additional bacteria or chemical tests, and have well defects or septic concerns assessed. Reducing contamination sources complements treatment; follow-up testing establishes whether the water has improved. CDC nitrate sources and additional testing