Well Water Testing in Minnesota: What to Test and How Often (MDH)

Well water testing in Minnesota

Short answer: The Minnesota Department of Health recommends testing a private well for coliform bacteria every year, nitrate every other year, and arsenic and lead at least once. Use a laboratory accredited by MDH.

Source: MDH, Well water testing (May 2025). Checked Nov 4, 2026.

As a private well owner, testing is up to you. Here is what to test for, how often, and where to send the sample.

What to test for

Test	How often	Why
Coliform bacteria	Every year	Shows whether germs can get into the well.
Nitrate	Every other year	Water over 10 mg/L should not be given to babies under six months old, MDH says.
Arsenic	At least once	About 10 percent of Minnesota wells are over the federal limit, mostly in western and south central Minnesota.
Lead	At least once	Most groundwater has none, but water can pick it up from old pipes, solder and fittings.

Schedule from MDH's well testing page. The notes on nitrate, arsenic and lead are from MDH's Well Owner's Handbook.

How to test

Get a sample bottle from an accredited lab. MDH's laboratory search lists them. Labs give you the containers and instructions.

Or ask your county. MDH says some county environmental or public health offices offer well water testing.

Follow the lab's instructions for taking the sample, and get it to the lab in time. Bacteria samples have a short time limit.

Test more often if nitrate shows up between 1 and 10 mg/L. MDH says to test at least once a year in that case.

If a test comes back high

Bacteria: the well may need to be disinfected, and a well company can look for how germs are getting in, like a damaged cap or casing.
Nitrate over 10 mg/L: MDH says to have the well inspected to see whether it was built right or is too close to a septic system or feedlot. Do not give the water to a baby under six months old.
Arsenic: it occurs naturally, and levels usually don't change much over time. Treatment or a different well may be needed.

Companies near you that name water testing on their website are on each county page (filter by "Water testing").

Sources: MDH, Well water testing (May 2025) · MDH, accredited laboratory search · MDH, Constructing a new water-supply well · MDH, Well Owner's Handbook (PDF, 2014)

Questions

How often should I test my well water in Minnesota?

MDH recommends testing for coliform bacteria every year and nitrate every other year, and for arsenic and lead at least once.

Where can I get my well water tested?

At a lab accredited by MDH. Search for one on MDH's accredited laboratory search, or ask your county's environmental or public health office whether it offers well water testing.

Does a new well get tested?

Yes. After building a well, the contractor must have the water tested for bacteria, nitrate and arsenic by an MDH-certified lab and send you the results.

Does boiling remove nitrate?

No. MDH says boiling makes nitrate more concentrated, because some of the water evaporates.