Well water in Door County, Wisconsin

In Door County, 11% of 194 private wells tested between 2003 and 2025 had total coliform above the Wisconsin limit (any detection), according to the UWSP Well Water Quality Viewer.

2,106 private wells tested 2003 to 2025 in state summaries; 1 individual samples from 1 wells, 1972 to 2008. Data refreshed September 9, 2026.

What homeowner tests found

Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 2003 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.

Contaminant	Wells tested	Above state level	Highest	State level
Total coliform	194	11%
Iron	136	11%	3,350	300 ug/L
E. coli	22	5%
Copper	167	3%	3.17	1.3 mg/L
Sodium	138	3%	281	20 mg/L
Arsenic	425	3%	51.2	10 ug/L
Lead	167	2%	46	15 ug/L
Chloride	194	2%	518	250 mg/L
Nitrate	2,106	1%	49.2	10 mg/L
Manganese	167	0%	179	300 ug/L

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What this means

Among homeowners in Door County who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (11% of 194 wells), E. coli (5% of 22 wells), and copper (3% of 167 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.

Iron exceeds the state's advisory level in a sizable share of wells; this is mostly a taste, staining or diet issue rather than a toxicity one.

What to test for in Door County

Volatile organic compounds (VOCs)125 leaking underground storage tank sites on record locally.
Total coliform11% of 194 local wells tested were above the Wisconsin limit (any detection).
Iron11% of 136 local wells tested were above the Wisconsin nuisance level.
E. coli5% of 22 local wells tested were above the Wisconsin limit (any detection).
Copper3% of 167 local wells tested were above the Wisconsin enforcement standard.
Sodium3% of 138 local wells tested were above the EPA advisory level.
Arsenic3% of 425 local wells tested were above the Wisconsin enforcement standard.
Lead2% of 167 local wells tested were above the Wisconsin enforcement standard.
Chloride2% of 194 local wells tested were above the Wisconsin nuisance level.

Contamination sources on record in Door County

Wisconsin DNR records 125 leaking underground storage tank sites in Door County, among 299 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.

125: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
34: lined landfills and transfer facilities
140: 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
Iron: Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Fluoride: Point-of-use reverse osmosis; Activated alumina; Distillation
Copper: Neutralizing filter to raise pH; Point-of-use reverse osmosis
Manganese: Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis

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Common questions

Is there arsenic in well water in Door County?

Arsenic was detected in 0% of 1 public well samples in Door County, 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 Door 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 Door County

Baileys Harbor0% nitrate
Brussels2% nitrate
Egg Harbor3% nitrate
Egg Harbor village0% nitrate
Ephraim village0% nitrate
Forestville<1% nitrate
Gardner3% arsenic
Gibraltar0% nitrate
Jacksonport<1% nitrate
Liberty Grove2% arsenic
Nasewaupee1% nitrate
Sevastopol6% total coliform
Sturgeon Bay0% nitrate
Union0% nitrate
Washington0% nitrate

4 towns have fewer than 30 public samples and are included in the Door County totals above rather than shown separately: Clay Banks, Forestville village, Sister Bay village, Sturgeon Bay.

Sources

USGS Water Quality Portal: 5 samples in Door 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 Door County, up to 2,106 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: 299 regulated sites located in Door 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.