Wisconsin well water testing: DNR recommendations and certified labs
Short answer: The Wisconsin DNR recommends testing a private well for bacteria and nitrate once a year and for arsenic once every five years, or yearly in Outagamie, Winnebago and Brown counties. Use a Wisconsin-certified lab, follow its sampling kit directions, and get bacteria samples to the lab within 48 hours.
The U.S. Geological Survey estimated that about 1.60 million people in Wisconsin supplied their own household water in 2015. USGS says the most common source of self-supplied water is a well. [source] [source]
The Wisconsin DNR says about one-quarter of the state's population drinks water from over 800,000 private wells. [source] The state health department says bacteria, nitrate and arsenic are three of the most common private well contaminants in Wisconsin. [source]
Recommended tests (DNR)
- Bacteria: once a year, and whenever taste, color or smell changes.
- Nitrate: once a year, and before the well is used by someone who is or may become pregnant.
- Arsenic: once every five years for most users; every year in Outagamie, Winnebago or Brown counties, or if arsenic turned up before. [source]
Reading results
The DNR says to stop drinking the water if bacteria are present. Above 10 mg/L nitrate, avoid drinking it if pregnant and don't give it to infants under six months. Above 10 parts per billion arsenic, DHS recommends not using the water for cooking foods that take up a lot of water. [source]
Where to test
Use a lab certified for the contaminant: see the DNR's certified laboratory lists. The lab provides the kit. Get the sample to the lab within the 48 hours the DNR says an accurate test requires. [source]
County guides
No county pages for this state yet. Your local health department is the first stop, per EPA guidance. [source]
FAQ
What tests does Wisconsin recommend for private wells?
The Wisconsin DNR recommends testing a private well for bacteria and nitrate once a year and for arsenic once every five years, or yearly in Outagamie, Winnebago and Brown counties. Use a Wisconsin-certified lab, follow its sampling kit directions, and get bacteria samples to the lab within 48 hours.
How many Wisconsin homes use private wells?
The Wisconsin DNR says over 800,000 private wells supply about one-quarter of the state's population.
How fast must a Wisconsin bacteria sample reach the lab?
The DNR says samples must reach the laboratory within 48 hours for an accurate test.
Sources
- USGS – Estimated Use of Water in the United States, County-Level Data for 2015 (domestic self-supplied population) (accessed 2026-10-23)
- USGS – Domestic Water Use (accessed 2026-10-23)
- Wisconsin DNR – Wells (accessed 2026-10-23)
- Wisconsin DNR – Test your private well water annually (accessed 2026-10-23)
- Wisconsin DNR – Certified laboratory lists (accessed 2026-10-23)
- Wisconsin DHS – What's in Your Water: Private Well Water Quality in Wisconsin (P-01830, PDF) (accessed 2026-10-23)
- US EPA – Protect Your Home's Water (accessed 2026-10-23)
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