Nitrate in Wisconsin well water
In Wisconsin, 8% of 121,661 private wells tested between 1984 and 2026 had nitrate above the Wisconsin enforcement standard (10 mg/L), according to the UWSP Well Water Quality Viewer.
Nitrate reaches wells from fertilizer, septic systems and manure. Above the limit it can cause methemoglobinemia (blue baby syndrome) in infants under six months, and long-term exposure is associated with some cancers. Shallow and dug wells near farmland or dense septic systems are most at risk.
Check your nitrate number
Type the value from your lab report. It is compared to the Wisconsin enforcement standard and the EPA limit, the same way the full interpretation does it.
Test your Wisconsin well for nitrate
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
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Systems that remove nitrate
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Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For nitrate
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For nitrate
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.
Where to get a well tested for nitrate in Wisconsin: certified labs, state programs and prices.
By county, from homeowner tests
Share of private wells above the state guidance level (10 mg/L) in tests homeowners sent to the state lab, 1988 to 2025.
| County | Above state level | Wells tested | Highest |
|---|---|---|---|
| Rock | 2,220 | 64.4 mg/L | |
| Portage | 3,842 | 76 mg/L | |
| Trempealeau | 894 | 48.2 mg/L | |
| Green Lake | 1,317 | 52.1 mg/L | |
| Pepin | 390 | 39.5 mg/L | |
| Columbia | 2,862 | 48.1 mg/L | |
| Dane | 7,299 | 127 mg/L | |
| Dunn | 1,265 | 45.4 mg/L | |
| Green | 2,533 | 69.9 mg/L | |
| Calumet | 824 | 38.9 mg/L | |
| Sauk | 2,708 | 94.4 mg/L | |
| La Crosse | 1,208 | 39.2 mg/L | |
| Pierce | 1,818 | 37.8 mg/L | |
| Chippewa | 2,684 | 34.9 mg/L | |
| St. Croix | 3,738 | 40.4 mg/L |
Towns with the highest share above the state level
- La Prairie, Rock County76% of 67 wells
- Caledonia, Trempealeau County69% of 68 wells
- Pine Grove, Portage County62% of 61 wells
- Leeds, Columbia County62% of 90 wells
- Kingston, Green Lake County60% of 149 wells
- Plainfield, Waushara County53% of 66 wells
- Richfield, Adams County53% of 34 wells
- Trempealeau, Trempealeau County48% of 145 wells
- Janesville, Rock County46% of 50 wells
- Arlington, Columbia County46% of 74 wells
- Plover, Portage County45% of 205 wells
- Buena Vista, Portage County45% of 150 wells
- Cottage Grove village, Dane County44% of 45 wells
- Plymouth, Rock County42% of 45 wells
- Scott, Columbia County41% of 94 wells
- Spring Green, Sauk County40% of 226 wells
- Buena Vista, Richland County39% of 128 wells
- Hampden, Columbia County39% of 57 wells
- Holland, La Crosse County39% of 236 wells
- Almond, Portage County38% of 126 wells
- Turtle, Rock County38% of 90 wells
- Harmony, Rock County37% of 117 wells
- Lincoln, Adams County36% of 66 wells
- Bradford, Rock County36% of 36 wells
- DeForest village, Dane County36% of 36 wells
By county, from individual samples
Public monitoring samples against the EPA limit (10 mg/L); counties with at least 30 samples.
| County | Above EPA limit | Samples | Detected | Median | Highest |
|---|---|---|---|---|---|
| Marathon | 31 | 100% | 11 | 71 mg/L | |
| Marquette | 94 | 94% | 6.86 | 190 mg/L | |
| Waupaca | 110 | 81% | 5.48 | 180 mg/L | |
| Rock | 127 | 99% | 5.1 | 89 mg/L | |
| Clark | 41 | 98% | 4.6 | 32 mg/L | |
| Iowa | 76 | 97% | 3.4 | 66.4 mg/L | |
| Dunn | 68 | 84% | 4.75 | 62 mg/L | |
| Waushara | 107 | 91% | 4.7 | 176 mg/L | |
| Monroe | 33 | 61% | 0.72 | 66 mg/L | |
| Adams | 343 | 99% | 4.3 | 124 mg/L | |
| La Crosse | 94 | 80% | 0.69 | 70 mg/L | |
| Sauk | 119 | 96% | 6.09 | 54.5 mg/L | |
| Portage | 1,790 | 90% | 3.9 | 208 mg/L | |
| Chippewa | 59 | 95% | 4.5 | 58 mg/L | |
| Barron | 71 | 97% | 3.2 | 100 mg/L |
Sources
- Wisconsin Well Water Quality Viewer samples: Private well samples compiled by the UWSP Center for Watershed Science and Education from the DNR Groundwater Retrieval Network, DATCP surveys, the UWSP Water and Environmental Analysis Lab and county health programs, published in the Wisconsin Well Water Quality Viewer with Wisconsin DHS. Samples are located to the town, village or city they fall in; one result per well and parameter (the latest) so repeat samples do not double count; wells without a state well number are keyed by location. Shares are against Wisconsin NR 140 enforcement standards (arsenic 10 ug/L, nitrate 10 mg/L as N, manganese 300 ug/L, lead 15 ug/L, copper 1.3 mg/L) and the iron and chloride secondary levels. Many samples were submitted by homeowners with a reason to test, so shares can run above a random survey. Retrieved September 9, 2026.
- Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. nitrate counts and shares are listed on each county and town page with their sources.
Analysis: Nitrate in private wells, decade by decade, from the same public records.