Guide · Updated October 5, 2026

Radon in Wisconsin Well Water

Radon does not rust a Wisconsin sink. DNR calls it colorless, odorless, and tasteless. The glass can look ordinary while a certified lab still prints picocuries per liter on a water sheet. People mix that line up with the indoor-air number they already know. EPA’s radon hub gives an action guideline of 4 pCi/L for indoor air. That is air. It is not a well-water limit, and this site will not turn it into a health lecture.

Private wells are unregulated. DNR, DHS, EPA’s private-wells pages, and CDC’s well-testing guidance put the schedule on the owner. The Pennsylvania radon page is the peer-state version of the same air-versus-water split. This page does not read a sheet as a medical result and does not rank a brand.

Get a certified-lab radon-in-water result first

DNR’s radon-in-well-water page says to test household air first. If indoor air exceeds 4 pCi/L, DNR says to have the household water tested and to take steps that bring indoor air to 4 pCi/L or less. DHS quotes the same EPA advice: if you use a private well and indoor air is over 4 pCi/L, you may want to test the water.

WSLH’s price list says radon-in-water tests are generally not necessary unless air radon levels are high, and its homeowner page asks you to call the lab before you order.

Sampling technique matters. Radon is a gas. WSLH says it is easily lost from a bottle if collection is sloppy. The published kit is a 40 mL glass VOC vial with a septum cap, no preservative, no air bubbles, and a four-day hold from collection to lab receipt. Ask the lab about the bottle, the hold time, and whether they collect. Sample kitchen cold unless they tell you otherwise.

Start at this site’s Wisconsin certified-lab inventory. Chemistry certification is DNR. Bacteria certification is DATCP. A coliform certificate is not a radon-in-water credential. DNR’s January 2026 radiochemistry file states that Wisconsin does not offer direct certification for radiochemistry; it approves labs accredited by a government accrediting body to the TNI standard. WSLH is the published homeowner path — DNR also points to Wisconsin Radon Information Centers. Nationwide index: certified labs by state.

CDC’s well-testing guidance is the federal annual floor: total coliform, nitrates, total dissolved solids, and pH, using a state-certified lab. UW–Stevens Point’s well-water program says Wisconsin wants bacteria and nitrate every year, with other tests when land use or geology puts them on the list. Radon-in-water is that extra. Nitrates in Wisconsin Well Water is the yearly nitrate reading order.

A store kit is a screen. Well water test kits explains that split. 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 on the same sheet still goes to the health department. SpringWell is an official catalog URL, labeled application pending. SpringWell is not a radon-treatment brand on this page. See the disclosure.

Circle bacteria and nitrate first. Then read how to read a lab report.

Indoor-air 4 pCi/L is not a water number

EPA’s radon pages use 4 pCi/L as the indoor-air action guideline. DHS runs the state indoor-air program. A water result is picocuries per liter of water. An air result is picocuries per liter of air. Same unit name. Different samples. Different programs. If a salesperson compares your kitchen sheet to 4, they are mixing tests.

DHS’s radon-in-water page: for every 10,000 pCi/L in household water, a time average of about 1 pCi/L is added to indoor air. EPA’s archived drinking-water radon page uses the same idea at the proposed AMCL: 4,000 pCi/L in water contributes about 0.4 pCi/L to indoor air. Those are published transfer lines, not a private-well statute.

EPA proposed 300 and 4,000 pCi/L are comparison only

On November 2, 1999, EPA published a proposed National Primary Drinking Water Regulation for radon-222. The proposal named a maximum contaminant level of 300 pCi/L, an alternative maximum contaminant level of 4,000 pCi/L, and a maximum contaminant level goal of zero. Those numbers were written for community water systems if the rule had been finalized. Best available treatment in the proposal was aeration; granular activated carbon was named as a small-system / point-of-entry class.

The rule was never finalized. It is not a Safe Drinking Water Act limit on a private well. DHS says there is currently no EPA regulation for radon in drinking water. Use 300 and 4,000 only as published comparison lines.

Two other Wisconsin lines sit next to that framework. DNR: consider modifying the water supply if well-water radon is over 4,000 pCi/L. WSLH, citing WDHS: for a private-well owner, action is recommended only if radon-222 is 10,000 pCi/L or greater. Those are agency comparison lines, not a kitchen-tap statute. If the reporting limit sits at or above 300 pCi/L, ask for a lower one.

Granite country is not your well

DNR: radon levels are always low in surface water. The highest dissolved-radon concentrations are in groundwater flowing through granite or granitic sand and gravel, commonly in northcentral and northwestern Wisconsin. Every Wisconsin well has some dissolved radon. You cannot know whether yours is high without a test.

WSLH says almost all supplies have measurable radon-222, and that only the north-central part of the state is known to have significantly elevated levels. DHS reports a survey of more than 500 private wells on a statewide grid: none south of a line from La Crosse to Green Bay had radon over 5,000 pCi/L. That is a survey result, not a county ranking.

USGS Water-Resources Investigations Report 95-4088 sampled 29 reservation wells. Radon-222 ranged from 260 to 22,000 pCi/L (median 560). The highest concentrations were in crystalline bedrock wells in Shawano, Menominee, Forest, and Marathon counties. That is a research set, not a census of every Wisconsin kitchen tap. A geologic map is not your well.

Treatment class only after a sheet

Do not shop a tank because the township sits on granite, or because a neighbor’s basement air test was high. After you have a water number, the classes DNR and EPA name are aeration and granular activated carbon, installed as point-of-entry after the pressure tank. Point-of-use at one kitchen tap does not address radon that leaves the water at showers and washers. DNR: small carbon filters on a faucet or under a sink are inadequate for radon.

DNR calls aeration the most effective class and says the unit must be designed so iron, iron bacteria, or hardness do not foul it. GAC can work and often needs pretreatment. DNR: GAC filters may accumulate hazardous levels of radiation when treating water at 4,000 pCi/L and higher; spent filters may need careful handling and disposal. EPA’s archived drinking-water radon page is the same caveat: radioactivity collects on the carbon and can require special disposal.

Look a model up in the NSF drinking-water treatment-unit database. NSF is a claim on a listed model, not a badge this site awards. DNR also wants the system approved by the Department of Safety and Professional Services plumbing program. Do not treat SpringWell as a radon specification; it is an official catalog URL labeled application pending.

If bacteria is present, stop. Health department first. A radon class still has to sit in a sane treatment order after the pressure tank. DNR’s other options after a high water number: connect to a public utility, or to a neighbor’s well that has already tested low. Bottled water for drinking does not stop radon leaving the well water into household air. A replacement well is last-resort and does not guarantee a lower number.

Bottom line

Radon in Wisconsin well water is invisible in the glass and easy to confuse with indoor air. Test air first. If indoor air is over 4 pCi/L, order a certified-lab radon-in-water test from the Wisconsin inventory — WSLH’s VOC vial, no bubbles, four-day hold. Use the proposed 300 and 4,000 pCi/L water lines as comparison only; DNR’s “consider modifying” line is 4,000 pCi/L, and WSLH cites WDHS action at 10,000 pCi/L. Granite and crystalline bedrock raise the odds in north-central and northwestern Wisconsin. They do not replace a sheet. Treatment class — aeration or GAC, point-of-entry, with the GAC disposal and gamma caveat — comes after the number. Bacteria and nitrate still go to the health department. See the disclosure.

Updated 2026-10-05.