How to read a well water test report

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Our test results explainer does this for you: type in each number and unit from your report and it tells you how each one compares to the limit. The rest of this page explains what it's doing.

Check the unit before you read the number.

Most results on a well report come in 1 of 3 units. The Minnesota Department of Health and the EPA use these equivalents:

Each step down is 1,000 times smaller. So 0.010 mg/L and 10 µg/L are the same amount.

Labs don't always use the unit you expect. The EPA writes the arsenic limit as 0.010 mg/L, and many people know it as 10 µg/L. If your report says arsenic is 0.012 mg/L, that's 12 µg/L, which is over the limit.

"ND" and the less-than sign mean the lab didn't find it.

"ND" stands for "not detected." A result like "<0.003 mg/L" means the same thing. Penn State's example is an arsenic result of "less than 0.003 milligrams per liter," which is the lowest amount that lab's instrument could read.

That lowest amount goes by a few names: detection limit, reporting limit, or method detection limit. A "not detected" is good news as long as that limit is below the health limit. If a lab reports lead as "<20 µg/L," you only know it's under 20, and the EPA's action level is 15. Ask the lab to rerun it with a lower limit.

A "greater than" sign means the opposite. The result was too high for the lab to count exactly. You'll see this most often on bacteria tests.

Compare health results to these EPA limits.

These are the EPA's limits for public water systems. They don't legally apply to a private well. The EPA still tells well owners to retest and call the health department when a result goes over one.

The lead action level drops to 10 µg/L on November 1, 2027, under the EPA's updated lead rule.

Watch which nitrate number you're reading. The EPA limit of 10 mg/L is for nitrate measured as nitrogen, which labs write as "nitrate as N" or "nitrate-N." If your report uses a different form, ask the lab to convert it.

Read bacteria results as present or absent.

Bacteria results usually come back as "present" or "absent," or as a count per 100 mL (milliliters, about 3 ounces). For a drinking water well, the target for total coliform is none. Penn State describes the health standard as zero colonies.

If total coliform is present and E. coli is absent, surface water is probably getting in somewhere. Penn State says most coliform bacteria come from surface water. If E. coli is present, the water has been in contact with human or animal waste. Use bottled water for drinking until the well is fixed and a retest comes back clean.

Results like iron and pH are about taste and stains.

The EPA calls these secondary standards. They're guidelines for taste, color and odor, and the EPA says these levels aren't considered a health risk.

Going over one of these usually means stains, scale or a bad taste. Manganese is the exception. It also has health guidance: the Minnesota Department of Health uses 0.1 mg/L (100 µg/L) if a baby drinks the water and 0.3 mg/L for everyone else. Some results, like hardness, have no EPA number at all.

Here's what to do with each kind of result.

• Everything under the limits. Keep the report. Test again next year for bacteria and nitrate, so you can compare.
• Close to a limit. Retest. A single sample shows the water on one day, and levels in shallow wells can move after rain.
• Over a health limit. The EPA says to retest right away and contact your local health department. Use bottled water for drinking, cooking and baby formula until you know more.
• Bacteria present. Plan to shock chlorinate the well and retest. Penn State says to retest about 10 to 14 days after disinfecting.
• Over a taste or stain guideline only. No rush. Look at treatment options when you're ready.

Don't count on boiling for anything but bacteria. The EPA says boiling doesn't remove lead.

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