Wisconsin has one of the highest rates of private well reliance in the country, and also some of the most extensively documented regional well-water problems — particularly nitrate contamination in the agricultural “Central Sands” region and bacterial contamination in the karst (fractured limestone) geology of the state’s northeast, including Kewaunee County. Private wells are not regulated under the federal Safe Drinking Water Act, and testing is the well owner’s responsibility.
Why test
None of the contaminants below have a reliable taste, odor, or color at concerning levels — a well can taste completely normal while carrying bacteria or nitrate well above health-based guidelines, which is exactly what’s been documented in parts of Wisconsin.
What to test for
A baseline panel for a Wisconsin well should include:
- Total coliform bacteria and E. coli — a priority test in Wisconsin’s karst regions, where fractured bedrock close to the surface can let contamination reach groundwater more easily than in areas with thicker soil cover.
- Nitrate — a well-documented, significant concern in Wisconsin’s sandy agricultural regions, tied to fertilizer application on porous, fast-draining soils; especially important for households preparing infant formula with well water.
- Arsenic — naturally occurring arsenic has been documented in some Wisconsin groundwater, notably in parts of the northeast.
- Lead — mainly relevant to household plumbing rather than the source water.
How often to test
Given the documented severity of nitrate and bacterial issues in some Wisconsin regions, testing at least annually for bacteria and nitrate — EPA’s general guidance — is a reasonable minimum; wells in the Central Sands or karst northeast may warrant more frequent testing, which a local lab or county health department can advise on.
Where to find a certified lab
The Wisconsin Department of Natural Resources runs the state’s laboratory certification program, accrediting labs to test drinking water (along with other aqueous and non-aqueous samples) — see the source link above for the program’s certified-lab resources.
After you test
If a result comes back above a health-based guideline, see our filter guides for which technologies are certified to address that specific contaminant — nitrate in particular has common misconceptions worth reading before buying anything.