Well water in Washington, Wisconsin
In Washington, 2% of 205 private wells tested between 1988 and 2025 had nitrate above the Wisconsin enforcement standard (10 mg/L), according to the UWSP Well Water Quality Viewer.
205 private wells tested 2011 to 2022 in state summaries; 1 individual samples from 1 wells, 1971 to 1982. Data refreshed September 9, 2026.
What homeowner tests found
Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 2011 to 2022. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.
| Contaminant | Wells tested | Above state level | Median | 95th pct | Highest | State level | |
|---|---|---|---|---|---|---|---|
| Iron | 5 | 20% | 68 | 365 | 365 | 300 ug/L | |
| Total coliform | 19 | 11% | |||||
| Arsenic | 21 | 5% | 0 | 8 | 177 | 10 ug/L | |
| Nitrate | 205 | 2% | 0.19 | 3.7 | 18.1 | 10 mg/L | |
| Chloride | 18 | 0% | 2.2 | 17 | 17 | 250 mg/L | |
| Manganese | 6 | 0% | 4 | 29 | 29 | 300 ug/L | |
| Lead | 6 | 0% | 0 | 13 | 13 | 15 ug/L | |
| Copper | 6 | 0% | 0.214 | 0.819 | 0.819 | 1.3 mg/L | |
| Sodium | 5 | 0% | 1.6 | 2.51 | 2.51 | 20 mg/L | |
| E. coli | 2 | 0% |
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What this means
Among homeowners in Washington who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (11% of 19 wells), arsenic (5% of 21 wells), and nitrate (2% of 205 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.
What to test for in Washington
- Volatile organic compounds (VOCs)3 leaking underground storage tank sites on record locally.
- Total coliform11% of 19 local wells tested were above the Wisconsin limit (any detection).
- Arsenic5% of 21 local wells tested were above the Wisconsin enforcement standard.
- Nitrate2% of 205 local wells tested were above the Wisconsin enforcement standard.
- Coliform bacteriaRecommended for every private well, every year.
- FluorideDetected in 100% of local samples.
Contamination sources on record in Washington
Wisconsin DNR records 3 leaking underground storage tank sites in Washington, among 15 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.
- 3
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 1
- lined landfill or transfer facility
- 11
- 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
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
Get your Washington water tested at home
A licensed local water treatment company tests your tap water in your home, walks you through the numbers, and quotes treatment only if something needs fixing. Free, about 30 minutes, no obligation. Tell us what you need and we match you with a company that serves Washington.
Common questions
Is there arsenic in well water in Washington?
Arsenic was detected in 100% of 1 public well samples in Washington, and 0% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How often should I test a private well in Washington?
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.
Sources
- USGS Water Quality Portal: 2 samples in Washington. 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, up to 205 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: 15 regulated sites located in Washington. 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.