Private wells
Wisconsin well water: who's on a well and what to test for
People on private wells
1,801,800
Homes on wells
32.8%
Est. above arsenic limit
72,700
Every Wisconsin county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| Waukesha County | 150,200 | 35% | 2.7% | 0.2 | 147 ft |
| Dane County | 71,800 | 12% | 4.1% | 1.8 | 114 ft |
| Marathon County | 56,400 | 38% | 5.9% | 0.8 | n/a |
| Washington County | 52,900 | 37% | 2.7% | 0.2 | 172 ft |
| Racine County | 49,000 | 24% | 6.4% | 0.1 | 90 ft |
| St. Croix County | 45,700 | 45% | 2.2% | 2.4 | 144 ft |
| Walworth County | 45,000 | 45% | 7.1% | 0.5 | 120 ft |
| Kenosha County | 44,900 | 28% | 6.5% | 0.0 | 123 ft |
| Outagamie County | 42,900 | 21% | 9.9% | 0.2 | n/a |
| Brown County | 42,300 | 14% | 8.2% | 0.2 | 120 ft |
| Rock County | 36,700 | 22% | 3.4% | 1.5 | 103 ft |
| Chippewa County | 36,000 | 55% | 3.4% | 2.5 | 63 ft |
| Winnebago County | 35,400 | 20% | 14.3% | 0.1 | n/a |
| Ozaukee County | 34,900 | 37% | 4.1% | 0.1 | 167 ft |
| Fond du Lac County | 33,600 | 32% | 3.4% | 0.3 | n/a |
| Portage County | 33,300 | 46% | 4.2% | 4.0 | 88 ft |
| Wood County | 32,300 | 40% | 5.3% | 0.6 | 83 ft |
| Polk County | 31,500 | 72% | 3.7% | 2.1 | 96 ft |
| Sheboygan County | 31,500 | 25% | 5.9% | 0.1 | n/a |
| Dodge County | 31,200 | 36% | 7.1% | 0.5 | 113 ft |
| Jefferson County | 30,600 | 37% | 7.7% | 0.4 | 108 ft |
| Waupaca County | 30,500 | 60% | 8.5% | 1.1 | 100 ft |
| Oconto County | 29,100 | 80% | 4.0% | 0.3 | n/a |
| Oneida County | 28,500 | 83% | 2.5% | 0.2 | 60 ft |
| La Crosse County | 28,200 | 22% | 2.5% | 1.6 | n/a |
| Barron County | 27,200 | 60% | 2.8% | 1.9 | 78 ft |
| Eau Claire County | 26,200 | 23% | 2.6% | 4.0 | n/a |
| Manitowoc County | 25,800 | 30% | 15.5% | 0.2 | 140 ft |
| Sauk County | 25,700 | 40% | 5.0% | 2.4 | n/a |
| Columbia County | 25,500 | 45% | 4.5% | 1.9 | 123 ft |
| Shawano County | 25,500 | 62% | 6.9% | 0.8 | 61 ft |
| Dunn County | 24,000 | 54% | 2.9% | 3.6 | n/a |
| Marinette County | 23,800 | 68% | 1.9% | 0.3 | 81 ft |
| Monroe County | 22,700 | 46% | 3.2% | 1.8 | n/a |
| Clark County | 22,400 | 61% | 4.2% | 0.3 | n/a |
| Milwaukee County | 20,100 | 2% | 3.7% | 0.0 | n/a |
| Waushara County | 19,900 | 87% | 3.5% | 2.2 | 100 ft |
| Vilas County | 19,800 | 92% | 2.6% | 0.2 | 61 ft |
| Pierce County | 19,700 | 48% | 1.9% | 1.5 | n/a |
| Door County | 19,700 | 70% | 4.9% | 0.1 | n/a |
| Grant County | 19,500 | 38% | 3.8% | 1.4 | n/a |
| Vernon County | 18,500 | 57% | 3.0% | 1.2 | n/a |
| Adams County | 16,900 | 88% | 4.7% | 1.1 | 63 ft |
| Lincoln County | 16,800 | 64% | 3.2% | 0.3 | 53 ft |
| Green County | 16,700 | 42% | 3.1% | 1.9 | n/a |
| Douglas County | 16,700 | 43% | 4.7% | 0.0 | 114 ft |
| Juneau County | 16,100 | 65% | 5.3% | 1.1 | 46 ft |
| Trempealeau County | 16,000 | 51% | 3.0% | 4.0 | n/a |
| Taylor County | 14,100 | 70% | 3.8% | 0.3 | n/a |
| Sawyer County | 14,100 | 85% | 1.8% | 0.3 | 63 ft |
| Marquette County | 13,800 | 89% | 9.4% | 1.5 | 113 ft |
| Burnett County | 13,500 | 88% | 2.7% | 0.4 | 76 ft |
| Jackson County | 13,000 | 65% | 2.3% | 2.4 | n/a |
| Washburn County | 12,100 | 80% | 2.2% | 0.6 | 95 ft |
| Kewaunee County | 11,900 | 56% | 14.8% | 0.3 | n/a |
| Bayfield County | 11,700 | 78% | 2.5% | 0.1 | 135 ft |
| Calumet County | 11,700 | 23% | 9.3% | 0.2 | n/a |
| Langlade County | 11,500 | 66% | 4.4% | 1.8 | 79 ft |
| Green Lake County | 10,800 | 60% | 3.9% | 1.2 | n/a |
| Iowa County | 10,700 | 45% | 2.8% | 1.3 | n/a |
| Richland County | 10,300 | 60% | 3.0% | 1.5 | n/a |
| Price County | 9,700 | 76% | 2.5% | 0.2 | n/a |
| Rusk County | 9,600 | 72% | 2.1% | 0.4 | 60 ft |
| Buffalo County | 9,100 | 66% | 3.0% | 1.9 | n/a |
| Lafayette County | 8,400 | 47% | 3.7% | 1.6 | n/a |
| Crawford County | 8,100 | 54% | 3.6% | 0.6 | n/a |
| Ashland County | 6,700 | 48% | 2.9% | 0.1 | 92 ft |
| Forest County | 6,500 | 81% | 2.7% | 0.3 | 81 ft |
| Pepin County | 4,800 | 62% | 2.4% | 3.1 | n/a |
| Florence County | 3,800 | 88% | 2.5% | 0.2 | 65 ft |
| Iron County | 3,700 | 70% | 2.2% | 0.1 | n/a |
| Menominee County | 2,800 | 68% | 4.3% | 0.2 | 58 ft |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Most well users above the arsenic limit
- Waukesha County: about 4,200 people
- Winnebago County: about 3,000 people
- Marathon County: about 2,700 people
- Kenosha County: about 2,500 people
- Racine County: about 2,400 people
Highest modeled nitrate
- Eau Claire County: 4.0 mg/L average (limit 10)
- Trempealeau County: 4.0 mg/L average (limit 10)
- Portage County: 4.0 mg/L average (limit 10)
- Dunn County: 3.6 mg/L average (limit 10)
- Pepin County: 3.1 mg/L average (limit 10)
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
Mail-in certified lab well water test
Mid-range2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
5-micron whole-house sediment filter
Budget3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
Air-injection iron and sulfur filter
Premium4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
12 GPM whole-house UV purifier
Premium5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
Waterdrop G3P600 tankless RO
Price at Waterdrop, checked Oct 5, 2026or compare on Amazon
iSpring RCC7AK reverse osmosis
Mid-range6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Waterdrop WHF21 2-stage whole-house filter
Mid-rangeQuestions
Which Wisconsin counties rely most on wells?+
By share of homes: Vilas County (92%), Marquette County (89%), Florence County (88%), Adams County (88%), Burnett County (88%). By number of people: Waukesha County (150,200), Dane County (71,800), Marathon County (56,400).
Is arsenic a problem in Wisconsin wells?+
USGS estimates about 72,700 Wisconsin well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Waukesha County, Winnebago County, Marathon County. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Wisconsin?+
We could not confirm a statewide rule for Wisconsin. Check with your county health department. Buyers can still make a lab test a condition of the offer.
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).