Guide · Updated September 19, 2026

Arsenic in Minnesota Well Water

A clear glass of Minnesota well water is not a test. Minnesota Department of Health’s Arsenic in Well Water page says you cannot taste, see, or smell arsenic, and that neighboring wells can still differ. The only number that counts is a certified-lab µg/L (or mg/L, converted). A county map, a neighbor’s well, or a catalog is not a diagnosis.

This page is a reading order for that sheet — not a medical consult and not a shopping list. MDH publishes health-effect language on its arsenic page. This site does not reprint that list and will not turn a µg/L into a risk score. If the number is high or the units are unclear, take the sheet to MDH or the county health department.

Private wells are unregulated. MDH’s Well Testing, Results, and Options page, EPA’s private-wells pages, and CDC’s well-testing guidance put the schedule on the owner. Nobody mails you a Consumer Confidence Report.

What 10 µg/L means — and what it is not

EPA’s National Primary Drinking Water Regulations and the Arsenic Rule set a public-water-system MCL of 10 µg/L (10 ppb / 0.010 mg/L). That is a Safe Drinking Water Act limit for community systems. Private wells are not under that Act. Do not call 10 µg/L a kitchen-tap legal limit.

MDH uses the same concentration as a teaching comparison. The tips-page arsenic line: any level of arsenic may be harmful, and MDH highly recommends taking protective action if the level is above 10 µg/L. EPA’s public-system MCL goal is 0 µg/L — a non-enforceable goal, not a private-well statute.

Units. µg/L and ppb match. 0.010 mg/L = 10 µg/L. Convert mg/L before you compare. If the reporting limit sits at or above 10 µg/L, ask for a lower one. How to read a well water lab report is the decoder.

How often MDH says to test

On MDH’s Well Testing, Results, and Options page — the same table as the March 2024 “five common contaminants” note:

• Every year: coliform bacteria and nitrate.
• At least once: arsenic, lead, and manganese — manganese especially before a baby drinks the water.

The arsenic page adds a construction wrinkle. As of August 2008, licensed contractors test each new well for arsenic and share the result with the owner and MDH. MDH still wants at least one test beyond that first sample. A non-detect on the first bottle means later arsenic is unlikely. A detect can rise or fall in the first months — consider a retest about six months after construction. Wells built since 2008 may already have a result in the Minnesota Well Index.

If you treat, MDH wants the bottle after treatment — the tap you cook and drink from. Need a raw-side number for a design? Ask for a second bottle.

CDC’s annual backbone is still coliform and nitrate every year, then add-ons when geology or the state program says so. In Minnesota, arsenic is that add-on. USGS Circular 1332 is the national domestic-well backdrop: arsenic showed up above human-health benchmarks in that study. A national paper is not your well.

Bacteria or nitrate on the same sheet goes to the health department first. Do not shop an arsenic stage while those lines are open.

A statewide percent is not your well

MDH: arsenic occurs naturally in Minnesota rock and soil. It has been detected in about 40 percent of new wells since 2008 (detection usually 2 µg/L). About 10 percent of private wells are above 10 µg/L. Some wells have been reported as high as 350 µg/L. Glacial history makes some areas more likely. Neighboring holes still differ.

Those percents are published occurrence, not a town ranking. Your well is not a map. The Maine arsenic, Texas arsenic, and Wisconsin arsenic pages are the peer-state versions of the same split.

Get a certified-lab µg/L — not a store-kit guess

Start at this site’s Minnesota certified-lab inventory. Accreditation is by analyte. A coliform certificate is not an arsenic certificate. Open MDH Search for Accredited Laboratories (ELDO; health.state.mn.us/labsearch). Customized Searches → Program: Safe Drinking Water Program → analyte: arsenic → check “Accepts samples from private homeowners” → Search. Then call about bottles and hold times.

The July 2026 PDF Accredited Labs in Minnesota Accepting Drinking Water Samples from Private Well Users is a snapshot of labs that take a homeowner bottle for coliform, nitrate, arsenic, lead, and/or manganese. An asterisk means a subcontract. A star means a courier or drop-off — ask the lab. Confirm current fields in ELDO before you pay.

Sample the cooking and drinking tap. Untreated: usually kitchen cold. Treated: after the tank, unless the lab says otherwise.

A store kit is a screen. Well water test kits explains that split. Nationwide index: certified labs by state. Lab news: /labs/minnesota/news. Sibling pages: Nitrates in Minnesota Well Water; Manganese in Minnesota Well Water.

After the sheet: classes, not a catalog

Name the class after you have a µg/L. Then look the model up in the NSF drinking-water treatment-unit database. NSF is a claim on a listed model — often NSF/ANSI 58 for reverse osmosis — not a badge this site awards. This page does not rank brands.

MDH names the classes people ask about:

• Point-of-use reverse osmosis (drinking and cooking). Look for NSF/ANSI 58 listings that name arsenic.
• Adsorptive media — a charged bed. NSF DWTU often lists iron-oxide or titanium-dioxide class claims. Read pH range and replacement interval.
• Anion exchange, where the sheet and a licensed installer say it fits. Salt regenerates the resin. That is not a hardness softener.

MDH also lists distillation and oxidation-plus-filtration. Still classes, not catalogs. A conventional softener or an activated-carbon filter alone will not remove arsenic. Boiling concentrates it. Treatment order after the pressure tank: sediment first, then the arsenic class, then a softener last if hardness remains.

If bacteria is present, stop. Health department first.

In Minnesota, MDH says treatment systems must be installed by a licensed and bonded plumbing or water-conditioning contractor, except that homeowners may install equipment in homes they own and occupy. Test the treated tap. Well Management: 651-201-4600 or 800-383-9808, health.wells@state.mn.us.

Mail-in certified-lab kits

Tap Score / SimpleLab is an approved class example of a mail-in certified-lab kit — not a ranked pick. Pair it with a lab from /labs/minnesota. Bacteria or nitrate still goes to the health department. See the disclosure.

What to do this week

1. Open /labs/minnesota. Confirm arsenic on the current ELDO certificate (Safe Drinking Water Program, accepts private homeowners).
2. If the well was drilled after August 2008, look up the construction arsenic result in the Minnesota Well Index or ask MDH — then plan the “at least once” retest MDH still wants.
3. Sample the cooking/drinking tap. If you treat, sample after treatment unless the lab says otherwise. Ask about bottle type and hold time.
4. Put the µg/L next to 10. Convert mg/L first. MDH highly recommends action above that line; any detect still belongs with MDH or the county if you cannot read the sheet. Well Management: 651-201-4600.
5. If bacteria or nitrate is also flagged, call the health department before you shop an arsenic stage.
6. Only after the sheet: decide point-of-use RO versus adsorptive media versus anion exchange, then NSF lookup. Not a softener. Not a pitcher “for arsenic.”

Bottom line

Arsenic is one of MDH’s five common private-well contaminants and invisible in the glass. About one in ten Minnesota private wells is above 10 µg/L on MDH’s published occurrence line. Order a certified-lab arsenic test from the Minnesota inventory. Compare µg/L to EPA’s public-system MCL of 10 — as a teaching number, not a private-well legal limit. MDH highly recommends action above that line. Treatment class comes after the sheet. Bacteria and nitrate still go to the health department.

Updated 2026-09-19.