Well Water Test Results Explained

Answer a few questions about your lab report and see the most urgent result first, what to do now, and when to call a well pro.

What each result means, most urgent first

Each result is checked against EPA and USGS benchmarks: bacteria should be absent, nitrate under 10 mg/L as nitrogen, iron under 0.3, manganese under 0.05, pH between 6.5 and 8.5.

Call a local well contractor first

E. coli means something is getting into the well. A pro should find the cause before you treat. Use bottled or boiled water until the well tests clean. Use bottled water for infant formula.

Treat the well, then retest

Coliform without E. coli usually responds to treating the well. Treat it, flush it, and test again about a week later. If it comes back, call a pro.

Test for E. coli, or call a well pro first

Coliform alone does not tell you how serious it is. Ask the lab to test the same sample for E. coli, or call a well pro before you treat. Use bottled or boiled water until you know. Use bottled water for infant formula.

Use safe water for infants, then get treatment advice

Nitrate does not come out with a standard filter, and boiling makes it more concentrated. Use a safe water source for infants, and ask your local health department about your options. A local water treatment pro can price a system that removes nitrate.

Use another water source for infant formula

Your manganese is above EPA's health advisory. Use another water source for formula, ask your health department, and ask a local pro what treatment removes manganese.

Test for bacteria first

You have not entered a coliform or E. coli result. Bacteria is the one problem you cannot see, smell or taste, so test for it before you spend money on anything else.

Test for nitrate before a baby drinks this water

Minnesota Department of Health says to test for nitrate when you plan a pregnancy or an infant will use the water. Babies under six months should not drink well water over 10 mg/L as nitrogen. Use bottled water for formula until you know.

Ask the lab for a lower reporting limit

One of your results is reported as below a limit that is higher than the guideline. Ask the lab to rerun it with a lower reporting limit.

Check the unit of your hardness result

Your hardness number reads soft in mg/L but hard in grains per gallon. Find the unit next to the number on your report (ppm is the same as mg/L), or ask the lab.

Match a treatment system to iron and manganese

Staining and a metallic taste come from dissolved metals. The right filter depends on the form of the iron, so test before you buy.

Find where the sulfur smell starts

Smell cold water and hot water separately. A smell only in hot water often points at the water heater. A smell in both points at the well.

Hard water needs a softener

A softener removes the calcium and magnesium that cause scale. Size it to your hardness number and household.

Get a fuller lab panel

Out-of-range pH or high TDS has many possible causes. A lab your state approves can test for metals and minerals so you treat the right thing.

Watch your nitrate trend

Your nitrate is under the limit, but past half of it. Retest every year, and test sooner after a flood or heavy fertilizer use near the well.

Test again next year

Nothing here needs action. EPA advises testing a private well every year for coliform bacteria, nitrate, TDS and pH.

How to read your report

Get a lab report. Use a lab your state approves. Ask for total coliform, E. coli, nitrate, iron, manganese, hardness, pH and total dissolved solids.
Say what the test checked. Bacteria only, a full panel, or minerals only. The explainer asks only about the results you have.
Pick each result and its unit. Bacteria is present or absent. Nitrate comes as nitrogen or as nitrate, hardness as mg/L or grains per gallon, manganese often as µg/L. If you do not know the unit, say so: nitrate is read the stricter way.
Say who drinks the water. A baby under six months or a pregnancy changes what nitrate means and what to test.
Start with the most urgent result. The result ranks your findings: bacteria and nitrate first, then missing tests, then stains and scale. Act now means a health risk. Watch means a nuisance. Unclear means the lab limit or unit was not enough to tell.

Private wells are not regulated by EPA, so these are the benchmarks agencies give owners, not legal limits for your tap.

Questions

What is a safe level of nitrate in well water?

EPA's limit is 10 mg/L as nitrogen. Above it, do not give the water to infants under six months or use it in formula. Boiling does not remove nitrate. If your lab reports nitrate as NO3, divide by 4.43 to get the nitrogen number.

What does a positive coliform test mean for a well?

Minnesota Department of Health says coliform in a water test can indicate that surface contamination has gotten into the water. Use boiled or bottled water for drinking and cooking (bottled only, never boiled, if your nitrate or manganese is high; and use bottled water for infant formula), treat the well, and test again to confirm it is clean.

Is E. coli in well water an emergency?

Treat it as one. E. coli points to fecal contamination. Do not drink the water until a well pro has found the cause and the well tests clean. Use bottled water in the meantime.

Are iron and manganese dangerous?

EPA sets them as secondary standards, iron at 0.3 mg/L and manganese at 0.05 mg/L. These are non-mandatory guidelines for taste, color and staining. Ask your state health department whether it has a separate health limit.

What pH should well water have?

EPA's guideline range is 6.5 to 8.5. Lower pH is acidic and can corrode pipes. Higher pH can leave scale.

How hard is hard water?

USGS calls 0 to 60 mg/L as calcium carbonate soft, 61 to 120 moderately hard, 121 to 180 hard, and over 180 very hard. One grain per gallon is about 17.1 mg/L.

How often should I test my well?

EPA says to test a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH. Test sooner after a flood, after work on the well, or if the taste or smell changes.

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Sources

General information, not medical advice. Ask your state or county health department about limits that apply to you.