Nitrate is common in Driftless-area wells. Wisconsin’s drinking water standard is 10 mg/L. If your well tests above that, state health officials say pregnant people and infants should switch to another water source right away. Boiling does not help; it concentrates nitrate. Options include bottled water, a certified treatment device, or a deeper, better-cased well.
Updated October 2026
What local studies found
These two studies used different methods and areas. Read them separately.
- Western Dane County, 2024 to 2025: 1,292 volunteer samples from 10 towns, including Mazomanie, Black Earth, Vermont, Blue Mounds, Perry, Primrose, Springdale, Cross Plains, Berry and Roxbury. 90% had detectable nitrate. 10% were over 10 mg/L. The highest was 26.7 mg/L.
- Southwest Wisconsin study (Grant, Iowa and Lafayette counties): in November 2018, 42% of 301 randomly chosen wells failed at least one standard: 34% for coliform bacteria, 4% for E. coli and 16% for nitrate over 10 mg/L. Across the whole study, 32% of 816 wells failed.
About 2 mg/L is natural background. Higher levels point to effects from land use, according to UW-Madison Extension monitoring.
Why Driftless wells are vulnerable
- Glaciers never covered this area, so there is little soil or glacial material over the bedrock.
- The bedrock is cracked dolomite and sandstone (karst), so water can move down quickly.
- State geologists rate the Driftless area highly susceptible to groundwater contamination.
Who is most at risk
- Infants.
- People who are pregnant.
- The Wisconsin Department of Health Services explains other health concerns on its nitrate page.
Treatment options
- Bottled water or another safe source for drinking, cooking and formula.
- A certified treatment device. Choose one certified to reduce nitrate, and keep testing the treated water. Installing treatment inside the house is plumbing work for a licensed plumber.
- A new or deeper, better-cased well, drilled by a DNR-licensed well driller. This can help, but results are not guaranteed.
- Not boiling. Boiling makes nitrate more concentrated.
Can a grant help?
- The state Well Compensation Grant covers nitrate only at 40 mg/L or higher, and only when the well serves livestock as well as the home.
- Household income must be $65,000 or less, with smaller awards from $45,000 to $65,000. You must apply before work starts.
- The ARPA well grant is closed.
- Free testing may be available through WellTAP. See grants and help.
When you need a licensed professional
- Drilling a new or deeper well: a DNR-licensed well driller.
- Installing treatment inside the house: a licensed plumber.
- Well repairs or disinfection if bacteria also show up: a licensed pump installer or driller.
Related
- Where to test well water
- Coliform or E. coli in your well
- Grants and financial help for well owners
- Typical well depths by town
- Getting a new well for a new home
Sources
