Well water in Sauk County, Wisconsin

In Sauk County, 13% of 2,708 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.

2,708 private wells tested 1988 to 2025 in state summaries; 15 individual samples from 5 wells, 1954 to 2019. Data refreshed September 9, 2026.

What homeowner tests found

Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 1988 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
Nitrate	2,708	13%	94.4	10 mg/L
Sodium	292	10%	201	20 mg/L
Total coliform	499	8%
Copper	347	6%	15.9	1.3 mg/L
E. coli	39	5%
Iron	287	4%	6,084	300 ug/L
Lead	345	3%	94	15 ug/L
Manganese	345	1%	3,885	300 ug/L
Arsenic	530	<1%	37.2	10 ug/L
Chloride	698	<1%	459	250 mg/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Sauk 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 1954 to 2019	15	93%	0%		0.238	0.657	30 ug/L EPA limit

Sampled fewer than 10 times, too few to summarize: Radium (226 + 228) (5), Fluoride (2), Nitrate (2), Arsenic (1), Copper (1), PFOA (1), PFOS (1), Radon (3), Manganese (2), Iron (1).

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What this means

Among homeowners in Sauk County who sent a sample to the state lab, the health-based limits most often exceeded were nitrate (13% of 2,708 wells), total coliform (8% of 499 wells), and copper (6% of 347 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 Sauk County

Volatile organic compounds (VOCs)112 leaking underground storage tank sites on record locally.
Nitrate13% of 2,708 local wells tested were above the Wisconsin enforcement standard.
Sodium10% of 292 local wells tested were above the EPA advisory level.
Total coliform8% of 499 local wells tested were above the Wisconsin limit (any detection).
Copper6% of 347 local wells tested were above the Wisconsin enforcement standard.
E. coli5% of 39 local wells tested were above the Wisconsin limit (any detection).
Iron4% of 287 local wells tested were above the Wisconsin nuisance level.
Lead3% of 345 local wells tested were above the Wisconsin enforcement standard.
Manganese1% of 345 local wells tested were above the Wisconsin enforcement standard.

Contamination sources on record in Sauk County

Wisconsin DNR records 112 leaking underground storage tank sites in Sauk County, among 438 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.

112: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
48: lined landfills and transfer facilities
278: other remediation projects

Treatment that fits the local profile

Nitrate: Point-of-use reverse osmosis; Anion exchange; Distillation
Total coliform: Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
Copper: Neutralizing filter to raise pH; Point-of-use reverse osmosis
E. coli: Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Sodium: Point-of-use reverse osmosis; Distillation
Fluoride: Point-of-use reverse osmosis; Activated alumina; Distillation

Get your Sauk County 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 Sauk County.

Common questions

Is there arsenic in well water in Sauk County?

Arsenic was detected in 100% of 1 public well samples in Sauk 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 high is radon in well water in Sauk County?

The median radon level across 3 public samples in Sauk County was 155 pCi/L, with a high of 680 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Sauk 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 Sauk County

Baraboo16% nitrate
Bear Creek3% nitrate
Dellona6% total coliform
Delton18% nitrate
Excelsior20% nitrate
Fairfield9% nitrate
Franklin2% nitrate
Freedom2% nitrate
Greenfield5% nitrate
Honey Creek8% nitrate
Ironton8% nitrate
La Valle22% total coliform
Merrimac8% total coliform
Prairie du Sac24% nitrate
Reedsburg20% nitrate
Spring Green40% nitrate
Troy8% nitrate
Washington5% nitrate
Westfield9% nitrate
Winfield9% nitrate
Woodland1% nitrate

18 towns have fewer than 30 public samples and are included in the Sauk County totals above rather than shown separately: Baraboo, Cazenovia village, Ironton village, Lake Delton village, La Valle village, Lime Ridge village, Loganville village, Merrimac village, North Freedom village, Plain village, Prairie du Sac village, Reedsburg, Rock Springs village, Sauk City village, Spring Green village, Sumpter, West Baraboo village, Wisconsin Dells.

Sources

USGS Water Quality Portal: 34 samples in Sauk 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 Sauk County, up to 2,708 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: 438 regulated sites located in Sauk 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.