Wisconsin well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Wisconsin county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 72 counties
- Waukesha CountyWell users 107,300Arsenic about 3 in 100Nitrate 0.2 mg/L
- Dane CountyWell users 54,000Arsenic about 4 in 100Nitrate 1.8 mg/L
- Marathon CountyWell users 50,700Arsenic about 6 in 100Nitrate 0.8 mg/L
- Racine CountyWell users 37,600Arsenic about 6 in 100Nitrate 0.1 mg/L
- Washington CountyWell users 37,100Arsenic about 3 in 100Nitrate 0.2 mg/L
- Walworth CountyWell users 35,300Arsenic about 7 in 100Nitrate 0.5 mg/L
- Outagamie CountyWell users 34,400Arsenic about 10 in 100Nitrate 0.2 mg/L
- St. Croix CountyWell users 34,400Arsenic about 2 in 100Nitrate 2.4 mg/L
- Rock CountyWell users 33,700Arsenic about 3 in 100Nitrate 1.5 mg/L
- Dodge CountyWell users 31,800Arsenic about 7 in 100Nitrate 0.5 mg/L
- Fond du Lac CountyWell users 31,300Arsenic about 3 in 100Nitrate 0.3 mg/L
- Winnebago CountyWell users 30,400Arsenic about 14 in 100Nitrate 0.1 mg/L
- Chippewa CountyWell users 29,900Arsenic about 3 in 100Nitrate 2.5 mg/L
- Portage CountyWell users 29,700Arsenic about 4 in 100Nitrate 4.0 mg/L
- Kenosha CountyWell users 29,400Arsenic about 7 in 100Nitrate 0.0 mg/L
- Sheboygan CountyWell users 28,300Arsenic about 6 in 100Nitrate 0.1 mg/L
- Wood CountyWell users 28,000Arsenic about 5 in 100Nitrate 0.6 mg/L
- Waupaca CountyWell users 27,800Arsenic about 8 in 100Nitrate 1.1 mg/L
- Polk CountyWell users 27,700Arsenic about 4 in 100Nitrate 2.1 mg/L
- Brown CountyWell users 27,500Arsenic about 8 in 100Nitrate 0.2 mg/L
- Jefferson CountyWell users 26,800Arsenic about 8 in 100Nitrate 0.4 mg/L
- Ozaukee CountyWell users 25,600Arsenic about 4 in 100Nitrate 0.1 mg/L
- Oneida CountyWell users 25,400Arsenic about 3 in 100Nitrate 0.2 mg/L
- Oconto CountyWell users 24,900Arsenic about 4 in 100Nitrate 0.2 mg/L
- Sauk CountyWell users 23,600Arsenic about 5 in 100Nitrate 2.4 mg/L
- Barron CountyWell users 23,600Arsenic about 3 in 100Nitrate 1.9 mg/L
- Shawano CountyWell users 23,200Arsenic about 7 in 100Nitrate 0.8 mg/L
- Manitowoc CountyWell users 23,100Arsenic about 16 in 100Nitrate 0.2 mg/L
- Clark CountyWell users 21,700Arsenic about 4 in 100Nitrate 0.3 mg/L
- Columbia CountyWell users 21,700Arsenic about 5 in 100Nitrate 1.9 mg/L
- Marinette CountyWell users 20,900Arsenic about 2 in 100Nitrate 0.3 mg/L
- Monroe CountyWell users 20,700Arsenic about 3 in 100Nitrate 1.8 mg/L
- Dunn CountyWell users 20,700Arsenic about 3 in 100Nitrate 3.6 mg/L
- Eau Claire CountyWell users 20,600Arsenic about 3 in 100Nitrate 4.0 mg/L
- Milwaukee CountyWell users 19,700Arsenic about 4 in 100Nitrate 0.0 mg/L
- La Crosse CountyWell users 18,600Arsenic about 2 in 100Nitrate 1.6 mg/L
- Waushara CountyWell users 18,500Arsenic about 4 in 100Nitrate 2.2 mg/L
- Pierce CountyWell users 18,000Arsenic about 2 in 100Nitrate 1.5 mg/L
- Grant CountyWell users 17,700Arsenic about 4 in 100Nitrate 1.4 mg/L
- Vilas CountyWell users 17,600Arsenic about 3 in 100Nitrate 0.2 mg/L
- Adams CountyWell users 16,300Arsenic about 5 in 100Nitrate 1.1 mg/L
- Door CountyWell users 16,200Arsenic about 5 in 100Nitrate 0.1 mg/L
- Green CountyWell users 16,000Arsenic about 3 in 100Nitrate 1.9 mg/L
- Douglas CountyWell users 15,500Arsenic about 5 in 100Nitrate 0.0 mg/L
- Vernon CountyWell users 15,400Arsenic about 3 in 100Nitrate 1.2 mg/L
- Juneau CountyWell users 15,200Arsenic about 5 in 100Nitrate 1.1 mg/L
- Lincoln CountyWell users 15,100Arsenic about 3 in 100Nitrate 0.3 mg/L
- Taylor CountyWell users 14,300Arsenic about 4 in 100Nitrate 0.3 mg/L
- Trempealeau CountyWell users 13,400Arsenic about 3 in 100Nitrate 4.0 mg/L
- Kewaunee CountyWell users 12,600Arsenic about 15 in 100Nitrate 0.3 mg/L
- Burnett CountyWell users 12,500Arsenic about 3 in 100Nitrate 0.4 mg/L
- Marquette CountyWell users 12,300Arsenic about 9 in 100Nitrate 1.5 mg/L
- Sawyer CountyWell users 12,000Arsenic about 2 in 100Nitrate 0.3 mg/L
- Calumet CountyWell users 11,500Arsenic about 9 in 100Nitrate 0.2 mg/L
- Jackson CountyWell users 11,200Arsenic about 2 in 100Nitrate 2.4 mg/L
- Washburn CountyWell users 11,100Arsenic about 2 in 100Nitrate 0.6 mg/L
- Langlade CountyWell users 11,000Arsenic about 4 in 100Nitrate 1.8 mg/L
- Iowa CountyWell users 10,000Arsenic about 3 in 100Nitrate 1.3 mg/L
- Bayfield CountyWell users 9,900Arsenic about 3 in 100Nitrate 0.1 mg/L
- Green Lake CountyWell users 9,800Arsenic about 4 in 100Nitrate 1.2 mg/L
- Price CountyWell users 9,500Arsenic about 3 in 100Nitrate 0.2 mg/L
- Richland CountyWell users 9,300Arsenic about 3 in 100Nitrate 1.5 mg/L
- Rusk CountyWell users 9,000Arsenic about 2 in 100Nitrate 0.4 mg/L
- Buffalo CountyWell users 8,700Arsenic about 3 in 100Nitrate 1.9 mg/L
- Lafayette CountyWell users 8,000Arsenic about 4 in 100Nitrate 1.6 mg/L
- Crawford CountyWell users 7,400Arsenic about 4 in 100Nitrate 0.6 mg/L
- Forest CountyWell users 6,400Arsenic about 3 in 100Nitrate 0.3 mg/L
- Ashland CountyWell users 5,300Arsenic about 3 in 100Nitrate 0.1 mg/L
- Pepin CountyWell users 4,500Arsenic about 2 in 100Nitrate 3.1 mg/L
- Florence CountyWell users 3,300Arsenic about 3 in 100Nitrate 0.2 mg/L
- Iron CountyWell users 2,800Arsenic about 2 in 100Nitrate 0.1 mg/L
- Menominee CountyWell users 2,300Arsenic about 4 in 100Nitrate 0.2 mg/L
Each mark = 1 in 100 well users the model places above 10 µg/L arsenic (scale 0–10)10 mg/L nitrate: the federal limit (MCL) for public systems
- These figures describe the area, not your well. Only a lab test shows what’s in your water.
- CDC says the Well Water Index figures “do not describe risk to individual wells.” (CDC Tracking Network)
- The arsenic model is better at spotting low-arsenic areas than at confirming high ones.
- Well-user counts are 2010 USGS estimates; tract values are averages over each census tract.
- Total coliform bacteriaEvery year
- NitrateEvery year
- Total dissolved solidsEvery year
- pHEvery year
- ArsenicAsk your local health department
EPA: Private Drinking Water Wells · CDC: Guidelines for Testing Well Water
Use a state-certified lab
Wisconsin Department of Natural Resources lists the laboratories certified to test drinking water in Wisconsin.
Screening tells you if something is worth a closer look
A lab result is the number you can act on.
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Lab-certified results
ETR Labs Basic Water Quality Test Kit
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
- Analyzed by Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638
- Turnaround: 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Screening: quick check, not lab-grade
Watersafe Drinking Water Test Kit
Silver Lake Research
Lead, bacteria, nitrate, copper, iron, chlorine, hardness and pH
- Turnaround: Minutes; the bacteria test can take up to 48 hours
What it can't tell you: Each test gives a yes/no or a rough range, not a lab number, and it cannot detect PFAS or arsenic.
A mail-in kit’s lab is accredited (ISO/IEC 17025) but may not be certified by your state. For a home sale, a loan, or a health-department follow-up, use a state-certified lab.
Wisconsin well water
Sources: CDC Well Water Index (2024) · USGS arsenic and nitrate models · USGS domestic well populations · EPA and CDC testing guidance. Data last updated 2026-10-08. All sources →
How many people use private wells in Wisconsin?
About 1.5 million people across 72 Wisconsin counties, by the USGS 2010 estimate. USGS models place about 73,500 of them in areas where wells are likely to be above the 10 µg/L arsenic limit. These are area estimates, not well results.
Are private wells regulated in Wisconsin?
The quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. (EPA) Testing and treatment are the owner's responsibility.
Where can I get my well tested in Wisconsin?
Wisconsin Department of Natural Resources keeps the list of laboratories certified to test drinking water in Wisconsin. Only use laboratories that are certified to do drinking water testing. (EPA)