Read a private well nitrate result in 5 steps

Read nitrate result from a private well: the short answer

The five steps in this guide walk you from the number on your report to the agency reference points that give it context. Step one confirms the laboratory and units. Steps 2 and 3 compare your figure with the 1, 3 and 10 mg/L levels. Steps 4 and 5 cover retesting and contacting your health department.

Your immediate task is simple: locate the nitrate concentration and its unit on your latest well test report, circle them, and write the 1, 3 and 10 mg/L reference points beside the number. This puts the agency figures directly next to your result so you can see where your number falls before you take the next step.

The 10 mg/L figure is the standard you compare against, as stated by the Minnesota Department of Health. The other reference points—1 mg/L and 3 mg/L—serve as earlier signals that may prompt closer attention or additional testing, depending on your specific situation.

Key takeaways

• Confirm the unit: Verify your report lists the concentration in mg/L (milligrams in a liter), which is equivalent to 1 ppm according to the Minnesota Department of Health.
• Check the 1 mg/L signal: If your result is above 1 mg/L, the Minnesota Department of Health suggests that additional testing may be a good idea.
• Interpret the 3 mg/L level: While 3 mg/L is below the EPA standard, it suggests human-made sources of nitrate may have contaminated the water and the level could increase over time, according to the Minnesota Department of Health.
• Identify natural baselines: Natural processes can cause low levels of nitrate in drinking water, usually less than 3 mg/L, as noted by the Minnesota Department of Health.
• Take action on high results: If your result exceeds the standard, contact your public health department and retest to confirm the finding.

Step 1: Confirm the laboratory and the units

Before comparing your number to any reference point, verify that the test came from a laboratory certified for drinking water testing. The U.S. Environmental Protection Agency advises that you use only laboratories certified to do this specific type of testing US EPA. If your report does not indicate the laboratory's certification status for drinking water, ask the lab or your health department how to confirm it. A result from an uncertified facility may not follow the protocols needed for a reliable comparison.

Once you have confirmed the lab, locate the specific concentration value for nitrate on the report. According to the U.S. Environmental Protection Agency, your water test results should include the concentration of the substances you tested for US EPA. Look for the line item labeled "nitrate" or "nitrate as nitrogen" and the unit mg/L, which is the unit the agency figures in this guide use. If the report uses another unit, such as ppm, note that 1 mg/L is equivalent to 1 ppm.

Check whether the report also states if the concentration exceeds a national primary or secondary drinking water standard. The U.S. Environmental Protection Agency notes that the report may include whether the substance concentration exceeds these standards US EPA. This notation helps you quickly see if your result falls above a regulatory limit. If the report does not include this comparison, you will perform the comparison yourself in the next steps using the reference points provided by agencies.

Steps 2 and 3: Compare your number with 1, 3 and 10 mg/L

Locate the concentration value on your report and place it beside the three reference points agencies publish. The Minnesota Department of Health defines the unit and provides the thresholds for comparison.

1 mg/L, or one milligram in a liter, is the same as 1 ppm. This definition helps you understand the scale of the number printed on your lab report. When your result shows a value above 1 mg/L, the Minnesota Department of Health suggests that additional testing may be a good idea. This threshold acts as an early signal to look closer at your water quality.

Natural processes can cause low levels of nitrate in drinking water, usually less than 3 mg/L. If your result is near 3 mg/L, the Minnesota Department of Health notes that while this is less than the EPA standard, it suggests human-made sources of nitrate may have contaminated the water. The agency also cautions that the level could increase over time. To put this in context, about 4 percent of private wells constructed in Minnesota since 1991 have nitrate levels above 3 mg/L. This statistic indicates that elevated levels are not rare in newer wells, making the 3 mg/L mark a useful watchpoint.

The Environmental Protection Agency (EPA) standard for nitrate in drinking water is 10 milligrams of nitrate (measured as nitrogen) in a liter of drinking water (mg/L). This is the regulatory ceiling you compare your result against. If your number exceeds 10 mg/L, it is above the standard. The Minnesota Department of Health identifies this figure as the EPA standard.

Write your result next to these three numbers. If your value is between 1 and 3 mg/L, note it as a potential trigger for further testing. If it is above 3 mg/L, mark it as a level that could rise and consider human-made sources. If it exceeds 10 mg/L, flag it immediately for the next steps.

Illustrative example: a 5 mg/L result

Suppose a report lists nitrate at 5 mg/L. That is above the 3 mg/L reference point, so it suggests human-made sources may have contaminated the water and the level could increase over time. It is still below the 10 mg/L EPA standard, so it does not exceed the standard. Keep the report on file and ask your health department about retesting.

Step 4 and 5: Retest and contact your health department

High levels of nitrate, defined as over 10 mg/L in water, can originate from runoff or leakage from fertilized soil, wastewater, landfills, animal feedlots, septic systems, or urban drainage, according to the Minnesota Department of Health. Understanding these potential sources helps you discuss specific local conditions with your health department when they advise on next steps.

The Minnesota Department of Agriculture Township Testing Program found that over 10 percent of the private wells sampled in some townships in southwestern, southeastern, central, and north-central Minnesota have nitrate levels above 10 mg/L, highlighting the prevalence of this issue in specific regions as noted by the Minnesota Department of Health. When your result is above the standard, your immediate next step is to call your local health department with your report in hand. They will guide you on the retest process and any necessary interim precautions for your household. Do not assume that a single test result provides a complete picture of your water quality over time; the retest confirms whether the high concentration is a persistent condition or a temporary anomaly. Keep your original lab report and the new retest results together so you have a clear record of the concentrations measured. For public water systems, see lead action levels for public water. If you have an infant under six months in the home, mention this explicitly to the health department, as EPA identifies infants below six months as the group that could become seriously ill from water above the 10 mg/L MCL. The health department can also advise on whether your local area has known sources of nitrate contamination that might affect your well.

Nitrate reference table by publisher

The table below lists the reference points and rules from each agency, using only the figures and statements found in their published guidance.

Keep this table with your lab report so you can quickly match your result to the relevant agency guidance.

What to keep on file with your result

Store your laboratory report with a note of the concentration and unit beside it. If your result is under 1 mg/L, keep the report on file and compare it with later results. If your result is near 3 mg/L, note it may suggest human-made sources and ask your health department about retesting. If an infant under six months drinks the water, contact your health department promptly about your result. Ingesting high levels of nitrate reduces the ability of red blood cells to carry oxygen, according to the Washington State Department of Health. The Wisconsin Department of Health Services provides a fact sheet, P-45012 (PDF), with information on certified treatment devices for nitrate. For help choosing among treatment options, see Home water treatment device: 5 checks before you buy.

Write the 1, 3 and 10 mg/L reference points beside your result.

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FAQ: reading well nitrate results

How do i read the nitrate result on my well water test?

Find the concentration in mg/L on a certified laboratory's report and compare it with the 1, 3, and 10 mg/L reference points agencies publish. US EPA states that water test results should include the concentration of the substances you tested for. If your result exceeds a standard, contact the public health department and retest to confirm the finding.

What does a nitrate result above 1 mg/L mean for my well?

Minnesota Department of Health says that a level above 1 mg/L suggests additional testing may be a good idea. Keep the report on file and compare it with later results to track changes over time.

Is 3 mg/L of nitrate in well water below the EPA standard?

Yes, 3 mg/L is less than the EPA standard of 10 mg/L. Minnesota Department of Health notes that this level suggests human-made sources of nitrate may have contaminated the water.

Which laboratory should i use to get a nitrate result i can compare?

US EPA advises using only laboratories certified to do drinking water testing. Check that the report lists the concentration of what was tested before comparing your number.

Who is most at risk from nitrate in drinking water?

Infants below the age of six months who drink water containing nitrate in excess of the MCL could become seriously ill. U.S. Environmental Protection Agency specifies that if untreated, these infants may die. Most adults are not at risk, according to the Washington State Department of Health.