Guide · Updated September 29, 2026

Arsenic in Wisconsin Well Water

A clear glass of Wisconsin well water is not a test. You cannot taste, see, or smell arsenic, and neighboring wells can still differ. The only number that counts is a certified-lab micrograms-per-liter (µg/L) result. 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. If the number is high or the units are unclear, take the sheet to your local health department or a licensed Wisconsin water professional.

Private wells are unregulated. The Safe Drinking Water Act does not cover them; testing and treatment are the owner’s job. EPA’s private-wells pages, Wisconsin DNR’s annual private-well testing page, and CDC’s well-testing guidance put the schedule on the owner. Nobody mails you a Consumer Confidence Report.

If you are on a city or utility system, look up that system’s Consumer Confidence Report through your water provider or Wisconsin DNR drinking water. That report is not a private-well sheet.

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.

Wisconsin DNR states the same federal drinking-water standard — 10 parts per billion — and notes that for private residential wells there is no state or federal requirement that you stop using the water at any level. Wisconsin DHS still recommends that if arsenic is more than 10 ppb, you stop using that water for drinking and for food preparation that takes up a lot of water.

Use 10 µg/L as a teaching comparison on a private-well sheet. 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.

Why Wisconsin wells pick up arsenic

Arsenic in Wisconsin groundwater is usually geologic — released from bedrock and soil minerals into the water — not a kitchen-sink spill. DNR’s arsenic program highlights naturally occurring arsenic statewide, with well-known elevated zones in parts of the Fox River valley, especially Outagamie and Winnebago counties (and nearby Brown), where sulfide minerals in the St. Peter sandstone and overlying rock can release arsenic when wells are drilled or when oxidation changes groundwater chemistry. An EPA case study on Outagamie and Winnebago special casing describes that same construction problem.

USGS models estimate the probability that private-well arsenic exceeds 10 µg/L across the conterminous United States. Those products are area risk models, not a reading for your wellhead. USGS Circular 1332 is the national domestic-well backdrop. A national paper is not your well.

A county average, a special-casing map, or a modeled “elevated risk” flag is published geography — not your well. Only a sample from your tap describes your water. This page will not invent a Wisconsin occurrence percent.

The Minnesota arsenic, Maine arsenic, and Texas arsenic pages are the peer-state versions of the same split: a map is not a kitchen tap.

How often to test

CDC’s annual backbone for private wells is still coliform bacteria and nitrate every year, then add-ons when geology or a state program says so. In Wisconsin, arsenic is that add-on.

Wisconsin DNR and DHS say most private-well users should test for arsenic at least once every five years. Test every year if you live in Outagamie, Winnebago, or Brown counties, or if a previous sample found arsenic. Pair that with annual bacteria and nitrate. DNR’s Tests for Private Well Users (DG-023) is the official list of which tests to run and when.

If you treat, sample the cooking and drinking tap after treatment unless the lab asks for a raw-side bottle. Bacteria or nitrate on the same sheet goes to the health department first. Do not shop an arsenic stage while those lines are open.

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

Start at this site’s Wisconsin certified-lab inventory. Chemistry certification is DNR; bacteria certification is DATCP. A coliform certificate is not an arsenic (metals) certificate.

Open DNR’s certified laboratory lists and the private-well testing page. Confirm drinking-water arsenic (or a total-metals method covering arsenic) on the current certificate, then call about bottles, hold times, and whether the lab accepts a private-well / residential sample. Nationwide index: certified labs by state. Lab news: /labs/wisconsin/news. Sibling page: Nitrates in Wisconsin Well Water.

Certified paths include a local or tribal health department, the Wisconsin State Laboratory of Hygiene, a University of Wisconsin lab, or a commercial lab. Households may be eligible for no-cost or low-cost testing through WellTAP — ask the local or tribal health department before you pay.

Sample the cooking and drinking tap. Untreated: usually kitchen cold. Treated: after the tank, unless the lab says otherwise. Use the lab’s bottle. Run the cold tap a few minutes first. Ship within the hold time.

A store strip kit is a screen. Well water test kits explains that split.

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/wisconsin. Bacteria or nitrate still goes to the health department. See the disclosure.

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.

Wisconsin DNR also points owners to Department of Safety and Professional Services–approved arsenic treatment devices (point-of-use and point-of-entry). Read the current list on DNR’s arsenic page before you buy.

Treatment classes people ask about for arsenic:

• Point-of-use reverse osmosis (drinking and cooking). Look for NSF/ANSI 58 listings that name arsenic.
• Adsorptive media — a charged bed (often iron-oxide or titanium-dioxide class claims on NSF DWTU lists). 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.
• Distillation at point of use, where a listed unit fits a single-tap case.

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.

A whole-house iron or sulfur filter is the wrong class for arsenic. Those catalogs stay off this page. Do not buy a pitcher “for arsenic.”

If bacteria is present, stop. Health department first. An arsenic cartridge on a contaminated well is the wrong Monday.

For extremely high results, DNR notes a new well with special construction may be needed. Outagamie and Winnebago counties sit in a Special Well Casing Depth Area with stricter casing, grouting, drilling method, and disinfection rules meant to reduce arsenic release during construction. Use a licensed Wisconsin well driller or pump installer. Retest the treated tap.

What to do this week

1. Open /labs/wisconsin. Confirm arsenic (metals) on a current DNR-certified drinking-water certificate for a lab that accepts private homeowners.
2. Sample the cooking/drinking tap. If you treat, sample after treatment unless the lab says otherwise.
3. Put the µg/L next to 10. Convert mg/L first. Above that public-system MCL line, follow DHS guidance on stopping drinking and food-prep use, and talk with your local health department if you cannot read the sheet.
4. If bacteria or nitrate is also flagged, call the health department before you shop an arsenic stage.
5. Only after the sheet: decide point-of-use RO versus adsorptive media versus anion exchange (or listed distillation), then NSF / DSPS lookup. Not a softener. Not a pitcher “for arsenic.”
6. Optional: ask your local health department about WellTAP — then confirm anything high at a DNR-certified lab.

Bottom line

Arsenic is invisible in Wisconsin well water and often geologic. Parts of the Fox River valley — especially Outagamie, Winnebago, and Brown — get extra state attention and annual retest advice. That is geography, not your wellhead. Order a certified-lab arsenic test from the Wisconsin inventory. Compare µg/L to EPA’s public-system MCL of 10 as a teaching number, follow DHS when the sheet is above that line, and name a treatment class only after the sheet. Bacteria and nitrate still go to the health department.

Updated 2026-09-29.