Arsenic in Wisconsin well water
In Wisconsin, 4% of 22,114 private wells tested between 1988 and 2025 had arsenic above the Wisconsin enforcement standard (10 ug/L), according to the UWSP Well Water Quality Viewer.
Arsenic occurs naturally in New England bedrock and dissolves into well water. Long-term exposure raises the risk of bladder, lung and skin cancers, and is linked to heart disease and lower IQ in children. It has no taste or smell, so testing is the only way to know.
Check your arsenic number
Type the value from your lab report. It is compared to the Wisconsin enforcement standard and the EPA limit, the same way the full interpretation does it.
Getting it fixed
Book a free in-home water test with a licensed local company, or see the treatment guide for what removes arsenic.
By county, from homeowner tests
Share of private wells above the state guidance level (10 ug/L) in tests homeowners sent to the state lab, 1989 to 2025.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Winnebago | 600 | 19% | 2,300 ug/L | |
| Outagamie | 403 | 19% | 4,300 ug/L | |
| Florence | 836 | 14% | 6,300 ug/L | |
| Shawano | 354 | 12% | 2,200 ug/L | |
| Marinette | 430 | 12% | 700 ug/L | |
| Ozaukee | 225 | 11% | 56 ug/L | |
| Menominee | 39 | 10% | 32 ug/L | |
| Dodge | 425 | 8% | 118 ug/L | |
| Walworth | 255 | 8% | 60.1 ug/L | |
| Lafayette | 118 | 8% | 74.8 ug/L | |
| Fond du Lac | 333 | 8% | 91 ug/L | |
| Jefferson | 1,178 | 7% | 94.8 ug/L | |
| Oconto | 434 | 7% | 129 ug/L | |
| Sheboygan | 220 | 7% | 36 ug/L | |
| Washington | 306 | 6% | 120 ug/L |
Towns with the highest share above the state level
- Center, Outagamie County45% of 67 wells
- Osborn, Outagamie County40% of 30 wells
- Algoma, Winnebago County39% of 147 wells
- Homestead, Florence County37% of 78 wells
- Niagara, Marinette County36% of 45 wells
- Morgan, Oconto County34% of 35 wells
- Emmet, Dodge County30% of 33 wells
- Cedarburg, Ozaukee County27% of 51 wells
- Matteson, Waupaca County27% of 30 wells
- Aurora, Florence County26% of 141 wells
- Angelica, Shawano County24% of 79 wells
- Clayton, Winnebago County22% of 101 wells
- Commonwealth, Florence County22% of 74 wells
- Watertown, Jefferson County20% of 70 wells
- Linn, Walworth County18% of 33 wells
- Fern, Florence County16% of 62 wells
- Milford, Jefferson County16% of 51 wells
- Norway, Racine County15% of 52 wells
- Ixonia, Jefferson County14% of 111 wells
- Farmington, Jefferson County14% of 63 wells
- Neenah, Winnebago County12% of 34 wells
- Winneconne, Winnebago County11% of 53 wells
- Hobart village, Brown County10% of 67 wells
- Tipler, Florence County10% of 58 wells
- Menominee, Menominee County10% of 39 wells
Sources
- Wisconsin Well Water Quality Viewer samples: Private well samples compiled by the UWSP Center for Watershed Science and Education from the DNR Groundwater Retrieval Network, DATCP surveys, the UWSP Water and Environmental Analysis Lab and county health programs, published in the Wisconsin Well Water Quality Viewer with Wisconsin DHS. Samples are located to the town, village or city they fall in; one result per well and parameter (the latest) so repeat samples do not double count; wells without a state well number are keyed by location. Shares are against Wisconsin NR 140 enforcement standards (arsenic 10 ug/L, nitrate 10 mg/L as N, manganese 300 ug/L, lead 15 ug/L, copper 1.3 mg/L) and the iron and chloride secondary levels. Many samples were submitted by homeowners with a reason to test, so shares can run above a random survey. Retrieved September 9, 2026.
- Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. arsenic counts and shares are listed on each county and town page with their sources.