Arsenic in Drinking Water in Wisconsin
What residents of Wisconsin need to know about arsenic in drinking water — including natural geological sources, private well risk, which utilities have documented violations, and how to remove arsenic from tap water.
Source: EPA SDWIS, Wisconsin Department of Natural Resources, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Wisconsin?
Yes — Wisconsin is among the top states in the Midwest for private well arsenic occurrence. The state's glacial aquifer systems and sandstone aquifer geology create conditions for naturally elevated arsenic in groundwater across a wide area of central and northern Wisconsin. Wisconsin DNR has documented arsenic as one of the most frequently detected contaminants above health guidelines in private well surveys, with certain counties showing very high occurrence rates.
Where does arsenic come from in Wisconsin's water?
Two primary pathways in Wisconsin: (1) Sandstone aquifer geology (the Cambrian Jordan and St. Peter sandstones, and the Paleozoic sandstone system) in central Wisconsin, where naturally occurring arsenic leaches from the rock, and (2) Glacial outwash and alluvial aquifer sediments in northern and central Wisconsin under reducing geochemical conditions. Private wells in these geological settings face the most direct risk.
What should Wisconsin residents know?
Wisconsin DNR has conducted extensive private well arsenic surveys and provides county-level data showing arsenic occurrence rates. Central Wisconsin counties — particularly those drawing from sandstone bedrock aquifers — have some of the highest documented private well arsenic rates in the Midwest. Wisconsin strongly recommends arsenic testing for all private well owners and provides subsidized testing programs.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Cambrian/Paleozoic sandstone aquifer (central WI); glacial outwash sediments (northern/central WI) |
| Occurrence rate | Some central WI counties show 20–30% of private wells exceeding MCL — among highest in Midwest |
| State program | DNR provides county-level arsenic occurrence maps and subsidized testing |
| State regulator | Wisconsin Department of Natural Resources (DNR) |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes risk |
| Effective treatment | Reverse osmosis or activated alumina; iron/manganese oxidation filters also used in WI iron-rich well water |
Why Arsenic Matters in Wisconsin
Wisconsin's arsenic problem is among the most significant in the upper Midwest. The state's Cambrian and Paleozoic sandstone bedrock aquifers, combined with its glacial outwash sediments, create widespread naturally elevated arsenic in groundwater. Wisconsin DNR has documented extremely high arsenic occurrence rates in some central Wisconsin counties — in some areas, 20–30% of private wells may exceed the MCL. The state has invested substantially in private well testing programs, public education, and has one of the more comprehensive county-level arsenic occurrence datasets available. Wisconsin also requires arsenic testing at certain well construction milestones.
Wisconsin Arsenic Program
Wisconsin DNR monitors arsenic under federal SDWIS and has conducted extensive arsenic mapping of the state's geology. Wisconsin's glacial aquifer system and sandstone aquifers in the central and western parts of the state are documented high-arsenic zones, with many wells exceeding 10 ppb. Wisconsin has one of the most active private well arsenic programs in the Midwest, including a Groundwater Coordinating Council arsenic mapping project. Private well owners in Adams, Portage, Marquette, and Wood counties face the highest risk.
Wisconsin Utilities With Arsenic Violation Records
The utilities listed below have at least one arsenic violation on record in EPA's SDWIS database. Violations may be open or resolved — see individual utility pages for current status and risk level.
How Does Arsenic Get Into Drinking Water?
Arsenic in drinking water is almost always naturally occurring — it leaches from arsenic-bearing rocks and minerals into groundwater over time. New England granite, Southwest volcanic geology, and Upper Midwest glacial aquifers are the primary high-risk formations. It has no taste, odor, or color.
Full arsenic overview — geology maps, health effects, all 50 statesWho Should Pay Closest Attention
Central Wisconsin counties drawing from sandstone aquifer systems — Wood, Portage, Waupaca, Waushara, Adams, Marquette, Green Lake, Fond du Lac — and northern Wisconsin counties with glacial outwash aquifer geology face the highest documented arsenic rates. Wisconsin private well owners statewide should test, but these counties are the highest priority.
Private well owners near mining districts or agricultural areas
Residents in states with documented volcanic or geothermal geology
Long-term consumers of water from small groundwater systems
Households in homes built before 1960 with older well casings
Residents whose well water has never been tested for arsenic
Anyone living in a state where bedrock wells are common
How to Check Your Situation in Wisconsin
- 1
Identify your water source. If you use a public utility, use the ZIP lookup on this page to find your system and check its compliance record.
- 2
If on public water, review your utility's most recent Consumer Confidence Report (CCR) for arsenic monitoring data. The MCL is 10 ppb — your report should show recent test results.
- 3
If on a private well, order an arsenic test from a Wisconsin Department of Natural Resources-certified laboratory. A basic arsenic test costs $15–$40. The state agency website maintains a certified lab list.
- 4
Test your well at the tap — not just at the wellhead. The entire water distribution system within your home can affect water quality.
- 5
If your test shows arsenic above 5 ppb, install certified treatment immediately. If above 10 ppb, do not use the water for drinking or cooking until treatment is installed.
- 6
Retest after installing treatment to confirm it is working as certified. Replace filter media on the manufacturer's schedule — an exhausted filter may not perform as rated.
Treatment Options for Arsenic
Boiling does not remove arsenic — it concentrates it. Standard activated carbon filters (Brita, etc.) do not effectively remove arsenic. Certified treatment is required.
NSF/ANSI Standard 58 — Reverse Osmosis
RO systems certified to NSF/ANSI 58 remove 85–95% of arsenic. Under-sink installation. Most effective for removing multiple contaminants simultaneously. Replace membranes and pre-filters on schedule.
Activated Alumina Filters
Activated alumina is specifically designed for arsenic and fluoride removal. Point-of-use or whole-house options available. Must be certified by NSF International or WQA for arsenic reduction. Requires periodic media regeneration or replacement.
Iron/Manganese Oxidation Filters
Effective for arsenic in iron-rich well water, which is common in the Midwest and New England. Oxidation converts dissolved iron and arsenic to a form that can be filtered out. Best when arsenic is co-occurring with high iron levels.
What does NOT work for arsenic
Standard activated carbon filters (Brita, refrigerator filters, most pitcher filters) do NOT effectively remove arsenic. Boiling concentrates arsenic. Water softeners do not remove arsenic. Only use products with NSF certification specifically for arsenic reduction.
Take Action Now
If you use a private well in Wisconsin, test for arsenic — especially if you are in a region with granite, volcanic, or sedimentary geology. A basic arsenic test costs $15–$40 at a state-certified lab.
Public water users: check your utility's Consumer Confidence Report (CCR) for arsenic results. The EPA MCL is 10 ppb — any detection warrants attention.
If arsenic is detected above 10 ppb (or even below it, given MCLG is zero), install an NSF/ANSI 58-certified reverse osmosis system for drinking and cooking water.
Standard carbon filters do NOT remove arsenic — do not rely on a Brita or refrigerator filter for arsenic protection.
Frequently Asked Questions
Related Pages
Arsenic — National Overview
All U.S. utilities with arsenic records
Wisconsin State Overview
All utilities and water quality data
Wisconsin Well Water Guide
Testing, risks & certified labs for private wells
Reverse Osmosis Guide
Removes 85–95% of arsenic
Best Arsenic Filter Guide
What actually works (carbon doesn't)
PFAS in Drinking Water
The 'forever chemical' contamination overview
All Contaminants
Complete reference library
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Find Your Utility
State Regulator
Wisconsin Department of Natural Resources ↗