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Wisconsin Water Quality Guide

Uranium in Wisconsin Drinking Water

Uranium in Wisconsin groundwater is a natural radionuclide — it comes from the same geology that produces radium and gross alpha, concentrated in the central part of the state.

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Federal limits and health goals

EPA legal limit (MCL)

0.030 mg/L

The federally enforceable maximum contaminant level. Above this, the system is in violation.

Health goal

5.0e-4 mg/L

A non-binding target representing minimal known risk over a lifetime of exposure.

What is uranium?

A naturally occurring radioactive metal found in rock formations. Both a chemical toxin and a radiation hazard.

Health effects

Increased risk of cancer, kidney toxicity

Where it comes from

Erosion of natural deposits

Wisconsin context

Uranium dissolves into groundwater from uranium-bearing rock formations, primarily in central Wisconsin. Marathon County is the geographic hot spot — multiple water systems in the Colby-Abbotsford area have recorded uranium levels near or above the federal MCL of 30 micrograms per liter. Unlike radium, which is regulated for its radioactivity (measured in picocuries per liter), uranium is regulated for its chemical toxicity to kidneys (measured in micrograms per liter). The 30 µg/L MCL is based on kidney damage risk, not cancer risk — though uranium is also radioactive.

For municipal systems, treatment options include ion exchange, reverse osmosis, and coagulation/filtration. Point-of-use reverse osmosis at the kitchen tap is effective for individual households. Uranium levels in groundwater are stable over time — if your system or well tests under the limit today, it will likely stay under. The systems that exceed tend to be in specific geological formations, not random.

Wisconsin systems above federal limits

1 active Wisconsin water system has recorded uranium readings above the EPA limit (0.030 mg/L) in monitoring data. Top 1 by most recent sample date:

COLBY WATERWORKS

Colby1,829 served

Most recent reading: May 2025

39.6

ug/L

Filtration that helps

Treatment categories that can reduce uranium in drinking water. Category-level only — no specific brands or models.

Reverse Osmosis

moderate cost

A membrane-based filtration process that forces water through a semi-permeable membrane under pressure. The membrane blocks dissolved solids, most metals, PFAS compounds, nitrate, and the majority of inorganic contaminants.

Limitations: Typically installed at point-of-use (under-sink), not whole-house

Anion Exchange

moderate cost

A resin-based process that swaps unwanted anions (nitrate, uranium, arsenic, perchlorate) in feed water for benign ions (typically chloride) on the resin surface. Different from cation exchange softening, which targets hardness minerals.

Limitations: Will not remove cations (calcium, magnesium, lead) — that's cation exchange softening

Frequently asked questions

Is uranium in my Wisconsin drinking water?
Uranium is widely detected at low levels across Wisconsin — about 276 systems have measurable amounts. But only a handful exceed the 30 µg/L federal limit, concentrated in Marathon County and a few other central Wisconsin locations. Check the list below for systems with readings above the EPA limit.
Is uranium in water radioactive?
Yes — uranium-238 is radioactive, but at the concentrations found in drinking water, the radiation dose is very small compared to natural background radiation. The EPA regulates uranium based on its chemical kidney toxicity, not its radioactivity. The 30 µg/L MCL protects against kidney damage from long-term daily exposure.
Does boiling remove uranium from water?
No — boiling concentrates uranium just like other dissolved minerals. Reverse osmosis is the most effective point-of-use treatment. Ion exchange systems also work but need proper maintenance to prevent uranium buildup on the resin.
Should I test my private well for uranium?
If you're in Marathon, Clark, or Wood counties, or if your well draws from granite or other crystalline bedrock, a one-time uranium test is worth doing. Cost is about $25–40 through a certified lab. Uranium levels are stable, so one test is usually sufficient unless you drill a new well.

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