Wisconsin Water Quality Guide

Arsenic in Wisconsin Drinking Water

Arsenic in Wisconsin drinking water comes from naturally arsenic-rich bedrock — primarily in the Fox River valley and the Sturgeon Bay region — and the EPA limit was tightened in 2006 because long-term exposure causes cancer.

A note from the author — I'm Jacob Thorwolf. WaterAdvantage.org is a personal project of mine, separate from my day job as an Account Executive at Bottleless Nation, a commercial water filtration company. If you request a consultation through any form on this site, it comes to me or a colleague at BN. More about this project →

Federal limits and health goals

EPA legal limit (MCL)

0.010 mg/L

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

Health goal

4.0e-6 mg/L

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

What is arsenic?

A naturally occurring element found in rocks and soil that can dissolve into groundwater. Even low levels are associated with increased cancer risk.

Health effects

Skin damage, circulatory problems, increased risk of cancer

Where it comes from

Erosion of natural deposits, runoff from orchards, runoff from glass and electronics production

Wisconsin context

Arsenic occurs naturally in some Wisconsin geology, especially in shallow groundwater drawn from aquifers with arsenic-bearing minerals. The Fox River Valley around Brown, Outagamie, and Winnebago counties, plus parts of the Door Peninsula, are the geographic hot spots. Concentrations in private wells in these areas have been measured anywhere from below detection up to 100 micrograms per liter — well over the federal MCL of 10 micrograms per liter.

Arsenic is a known human carcinogen. Long-term exposure even at low levels has been linked to skin, bladder, and lung cancers, plus cardiovascular disease. The 10 µg/L limit is the lowest the EPA could set while remaining technically and economically feasible — the actual health goal (MCLG) is zero. Treatment is straightforward at point-of-use (reverse osmosis), but municipal-scale treatment is expensive, which is why some smaller WI systems have struggled to meet the standard.

Wisconsin systems above federal limits

6 active Wisconsin water systems have recorded arsenic readings above the EPA limit (0.010 mg/L) in monitoring data. Top 6 by most recent sample date:

ELKHORN WATERWORKS

ELKHORN10,317 served

Most recent reading: Feb 2026

0.049

mg/L

FAIRWATER WATERWORKS

FAIRWATER365 served

Most recent reading: Aug 2025

0.014

mg/L

FOND DU LAC WATERWORKS

FOND DU LAC44,303 served

Most recent reading: May 2025

0.041

mg/L

CLINTONVILLE UTILITIES

CLINTONVILLE4,635 served

Most recent reading: Sep 2024

0.012

mg/L

GREENVILLE UTILITIES VIL OF

GREENVILLE11,340 served

Most recent reading: Apr 2024

6.57

mg/L

EMBARRASS WATERWORKS

EMBARRASS347 served

Most recent reading: Feb 2021

0.013

mg/L

Filtration that helps

Treatment categories that can reduce arsenic 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

Frequently asked questions

Is arsenic in my Wisconsin drinking water?

Geographically, arsenic is concentrated in Brown, Outagamie, Winnebago, and Door counties, plus a few hot spots elsewhere. If you're on a municipal system there, your annual water quality report will show arsenic results. If you're on a private well in these counties, get a one-time arsenic test — concentration doesn't change much year-to-year unless your well is new. The list further down shows WI municipal systems with documented health-based arsenic violations.

Does boiling water remove arsenic?

No — boiling actually concentrates arsenic by removing water and leaving the dissolved arsenic behind. The same is true for letting water sit out overnight. Arsenic removal requires reverse osmosis, distillation, or specialized adsorptive media (iron-based or activated alumina). Standard pitcher filters with carbon do not remove arsenic.

What does arsenic in drinking water actually do to you?

Long-term exposure (years to decades) at levels above the EPA limit increases the risk of bladder, lung, and skin cancer. It's also been linked to cardiovascular disease, type 2 diabetes, and developmental effects in children. Short-term high-dose exposure causes acute poisoning, but that's rare from drinking water at typical Wisconsin concentrations — the chronic risk is the real concern.

Is well water in Door County safe to drink?

It depends on the specific well. Door Peninsula geology includes arsenic-bearing dolomite, and individual well concentrations vary widely over short distances. If you're on a private well in Door County, test once for arsenic. If the result is over 10 µg/L, install point-of-use reverse osmosis on your kitchen sink. If it's under, you're done — concentration doesn't change unless the well is redrilled.

Curious about filtration for your home or facility?

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