Well water by county: Wisconsin
Across 69 counties in Wisconsin, 16 of 548 sampled wells (3%) were above the arsenic limit and 114 of 3524 (3%) above the nitrate limit. Updated 2026-10-17. Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well.
Share of sampled wells whose latest result is above the EPA limit (arsenic 10 µg/L, nitrate 10 mg/L as N).
| County | Arsenic > 10 µg/L | Nitrate > 10 mg/L |
|---|---|---|
| Adams County | 0% of 10 | 4% of 27 |
| Ashland County | 0% of 45 | 0% of 79 |
| Barron County | – | 6% of 53 |
| Bayfield County | – | 0% of 77 |
| Brown County | 2% of 45 | 1% of 103 |
| Buffalo County | – | 0% of 12 |
| Burnett County | 0% of 27 | 0% of 58 |
| Calumet County | – | 4% of 27 |
| Chippewa County | – | 3% of 31 |
| Clark County | – | 0% of 29 |
| Columbia County | – | 5% of 115 |
| Crawford County | – | 12% of 33 |
| Dane County | 16% of 25 | 8% of 131 |
| Dodge County | 0% of 10 | 2% of 108 |
| Door County | – | 0% of 38 |
| Douglas County | – | 0% of 94 |
| Dunn County | – | 9% of 43 |
| Eau Claire County | – | 0% of 31 |
| Florence County | – | 0% of 18 |
| Fond du Lac County | – | 4% of 45 |
| Forest County | 2% of 51 | 4% of 100 |
| Grant County | 0% of 13 | 6% of 50 |
| Green County | – | 7% of 27 |
| Green Lake County | – | 20% of 10 |
| Iowa County | 0% of 12 | 11% of 36 |
| Jackson County | – | 0% of 14 |
| Jefferson County | – | 0% of 80 |
| Juneau County | – | 7% of 15 |
| Kenosha County | 0% of 12 | 0% of 29 |
| Kewaunee County | – | 0% of 16 |
| La Crosse County | – | 6% of 51 |
| Lafayette County | – | 6% of 32 |
| Langlade County | 0% of 18 | 0% of 64 |
| Lincoln County | – | 0% of 22 |
| Manitowoc County | – | 2% of 54 |
| Marathon County | – | 31% of 13 |
| Marinette County | 14% of 14 | 0% of 34 |
| Marquette County | 0% of 11 | 16% of 19 |
| Menominee County | 3% of 36 | 1% of 70 |
| Milwaukee County | – | 0% of 78 |
| Monroe County | – | 11% of 19 |
| Oconto County | 0% of 10 | 0% of 20 |
| Oneida County | – | 0% of 14 |
| Outagamie County | – | 0% of 12 |
| Ozaukee County | – | 0% of 66 |
| Pepin County | – | 20% of 10 |
| Pierce County | – | 3% of 29 |
| Polk County | 0% of 12 | 0% of 55 |
| Price County | – | 8% of 13 |
| Racine County | 8% of 13 | 0% of 38 |
| Richland County | – | 0% of 16 |
| Rock County | – | 12% of 58 |
| Rusk County | – | 0% of 21 |
| Sauk County | – | 3% of 33 |
| Sawyer County | – | 0% of 22 |
| Shawano County | 4% of 46 | 8% of 92 |
| Sheboygan County | – | 4% of 69 |
| St. Croix County | – | 4% of 113 |
| Trempealeau County | – | 0% of 28 |
| Vernon County | – | 0% of 36 |
| Vilas County | 0% of 56 | 3% of 120 |
| Walworth County | 20% of 15 | 1% of 109 |
| Washburn County | – | 0% of 21 |
| Washington County | – | 1% of 123 |
| Waukesha County | 0% of 31 | 1% of 195 |
| Waupaca County | 6% of 17 | 15% of 20 |
| Waushara County | 0% of 19 | 14% of 29 |
| Winnebago County | – | 8% of 12 |
| Wood County | – | 3% of 165 |