Well water in Washington County, Wisconsin
In Washington County, 16% of 176 private wells tested between 2000 and 2025 had total coliform above the Wisconsin limit (any detection), according to the UWSP Well Water Quality Viewer.
1,857 private wells tested 2009 to 2025 in state summaries; 12 individual samples from 10 wells, 1961 to 2024. Data refreshed September 9, 2026.
What homeowner tests found
Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 2009 to 2025. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA. County and state figures combine the town summaries, weighted by wells tested; medians are not combined.
What individual samples found
Each row summarizes every public sample for that contaminant inside Washington County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| Uranium 1983 to 2024 | 12 | 58% | 0% | 0.109 | 1.4 | 30 ug/L EPA limit |
Sampled fewer than 10 times, too few to summarize: Nitrate (8), Radium (226 + 228) (5), Copper (3), Chloride (4), Manganese (3), Iron (3), Sodium (3), Radon (1).
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What this means
Among homeowners in Washington County who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (16% of 176 wells), arsenic (6% of 306 wells), and lead (5% of 73 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.
Sodium and iron exceed the state's advisory level in a sizable share of wells; these are mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Washington County
- Volatile organic compounds (VOCs)178 leaking underground storage tank sites on record locally.
- Sodium33% of 36 local wells tested were above the EPA advisory level.
- Iron28% of 36 local wells tested were above the Wisconsin nuisance level.
- Total coliform16% of 176 local wells tested were above the Wisconsin limit (any detection).
- Arsenic6% of 306 local wells tested were above the Wisconsin enforcement standard.
- Lead5% of 73 local wells tested were above the Wisconsin enforcement standard.
- Nitrate3% of 1,857 local wells tested were above the Wisconsin enforcement standard.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 280 pCi/L.
Contamination sources on record in Washington County
Wisconsin DNR records 178 leaking underground storage tank sites in Washington County, among 612 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 178
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 53
- lined landfills and transfer facilities
- 381
- other remediation projects
Treatment that fits the local profile
- Total coliform
- Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Lead
- Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
- Sodium
- Point-of-use reverse osmosis; Distillation
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
- Chloride
- Point-of-use reverse osmosis; Distillation
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Common questions
How high is radon in well water in Washington County?
The median radon level across 1 public samples in Washington County was 280 pCi/L, with a high of 280 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Washington County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Towns in Washington County
- Addison4% nitrate
- Barton0% nitrate
- Erin2% nitrate
- Farmington2% nitrate
- Germantown village0% nitrate
- Hartford8% nitrate
- Jackson8% nitrate
- Kewaskum0% nitrate
- Polk3% arsenic
- Richfield village6% arsenic
- Slinger village2% nitrate
- Trenton19% total coliform
- Wayne1% nitrate
- West Bend3% nitrate
7 towns have fewer than 30 public samples and are included in the Washington County totals above rather than shown separately: Germantown, Hartford, Jackson village, Kewaskum village, Milwaukee, Newburg village, West Bend.
Sources
- USGS Water Quality Portal: 42 samples in Washington County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- Wisconsin Well Water Quality Viewer samples: summaries for 10 contaminants in Washington County, up to 1,857 wells each. 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.
- Wisconsin DNR regulated sites: 612 regulated sites located in Washington County. Open and closed remediation activities (BRRTS, including leaking underground storage tanks and spills) and landfill and waste sites from the Wisconsin Department of Natural Resources. Retrieved September 9, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.