Well water in Walworth County, Wisconsin

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Testing recommended

private wells tested between 1990 and 2025 in Walworth County had arsenic above the Wisconsin enforcement standard (10 ug/L), according to the UWSP Well Water Quality Viewer.

1,692 private wells tested 2013 to 2020 in state summaries; 1,057 test results across 14 contaminants from at least 117 wells, 1945 to 2021; nitrate has the most at 202. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

An estimated 35,555 people in Walworth County get their drinking water from a private well, per USGS 2015 county water use. That is about 35% of residents.

Separately, the USGS national arsenic model estimates that 5% of the 35,555 people on private wells in Walworth County draw water above 10 ug/L (the model's range is 4% to 6%), from geology and well depth rather than local tests.

What homeowner tests found

Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 2013 to 2020. 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	Above state level	Wells tested	Highest	State level
E. coli	50%	2
Iron	15%	13	5,757	300 ug/L
Total coliform	9%	23
Arsenic	8%	255	60.1	10 ug/L
Sodium	8%	13	32.4	20 mg/L
Nitrate	5%	1,692	73.8	10 mg/L
Lead	5%	22	138	15 ug/L
Chloride	0%	23	236	250 mg/L
Copper	0%	22	0.516	1.3 mg/L
Manganese	0%	22	24	300 ug/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Walworth 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	Above limit	Samples	Detected	Median	Highest	Limit
Arsenic 1976 to 2021	17%	23	83%	1.2	14	10 ug/L EPA limit
Nitrate 1954 to 2021	4%	202	75%	0.111	71	10 mg/L EPA limit
Fluoride 1945 to 2021	0%	129	100%	0.2	1.7	4 mg/L EPA limit
Lead 1976 to 2021	0%	22	36%	0	0.09	15 ug/L EPA limit
Copper 1983 to 2021	0%	19	74%	0.001	0.02	1.3 mg/L EPA limit
Uranium 1983 to 2021	0%	19	74%	1.35	7.89	30 ug/L EPA limit
Radium (226 + 228) 1983 to 2001	0%	18	72%	0	3	5 pCi/L EPA limit
Iron 1945 to 2021	no limit	182	99%	870	10,000	300 ug/L nuisance level
Chloride 1945 to 2021	no limit	167	100%	2.5	615	250 mg/L nuisance level
Manganese 1945 to 2021	no limit	165	100%	30	480	300 ug/L health guideline
Sodium 1945 to 2021	no limit	102	100%	7.4	344	20 mg/L health guideline

Sampled fewer than 10 times, too few to summarize: PFOA (1), PFOS (1), Radon (7).

Over time

Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.

Contaminant	before 2000	2000s	2010s	2020s
Nitrate	5%174 samples	0%22 samples	n/a	n/a
Fluoride	0%114 samples	0%12 samples	n/a	n/a

Nitrate above the limit in Walworth County fell from 5% of 174 samples before 2000 to 0% of 22 in the 2000s.

Closer than the county

See the sampled wells near your address

The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.

Check my address

What this means

Among homeowners in Walworth County who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (9% of 23 wells), arsenic (8% of 255 wells), and nitrate (5% of 1,692 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 Walworth County

1
Arsenic
17% of 23 local samples were above the limit.
2
Total coliform
9% of 23 local wells tested were above the Wisconsin limit (any detection).
3
Nitrate
5% of 1,692 local wells tested were above the Wisconsin enforcement standard.
4
Lead
5% of 22 local wells tested were above the Wisconsin enforcement standard.
5
Coliform bacteria
Recommended for every private well, every year.
6
Radon
Median local reading is 220 pCi/L.
7
Iron
15% of 13 local wells tested were above the Wisconsin nuisance level.
8
Sodium
8% of 13 local wells tested were above the EPA advisory level.
9
Volatile organic compounds (VOCs)
136 leaking underground storage tank sites on record locally.

Test your Walworth County well for arsenic, total coliform and 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 $209 Already tested? Upload the report

Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.

Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.

Where to get a well tested in Wisconsin: certified labs, state programs and prices.

Already have results back? Get your lab report read against the Walworth County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

The rock under Walworth County

Silurian-Devonian aquifers

Carbonate-rock. Limestone and dolomite move water through cracks and solution channels, sometimes very fast. Bacteria and nitrate can travel from the surface to a well in days, so annual bacteria testing matters more here than most places; hardness is a given.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.

Official help in Wisconsin

Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.

Wells, Wisconsin DNR
Laboratory Certification, Wisconsin DNR

Contamination sources on record in Walworth County

Wisconsin DNR records 136 leaking underground storage tank sites in Walworth County, among 508 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.

136: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
47: lined landfills and transfer facilities
325: 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

Iron

Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration

Sodium

Point-of-use reverse osmosis; Distillation

Nitrate

Point-of-use reverse osmosis; Anion exchange; Distillation

Manganese

Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis

Systems we would look at first

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 total coliform

Aquasana Rhino Well Water with UV

whole-house, at the point of entry, about $2,871

Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.

For arsenic

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For arsenic

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

For arsenic

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.

For iron

Iron and manganese oxidizing filter

whole-house, at the point of entry, about $1,800

Air-injection or greensand media; fixes staining at the source.

Free, no obligation

Get on the list for a free in-home water test in Walworth County

No water treatment company serves Walworth County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Walworth County, and you get an email naming it first.

Common questions

Is there arsenic in well water in Walworth County?

Arsenic was detected in 83% of 23 public well samples in Walworth County, and 17% 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 Walworth 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 Walworth County

13 towns have fewer than 30 public samples and are included in the Walworth County totals above rather than shown separately: Burlington, Darien village, Delavan, East Troy village, Fontana-on-Geneva Lake village, Genoa City village, Lake Geneva, Mukwonago village, Sharon, Sharon village, Walworth village, Whitewater, Williams Bay village.

Counties near Walworth County

Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.

Want the numbers themselves? Download the Wisconsin dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 1,057 samples in Walworth 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 Walworth County, up to 1,692 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.
USGS national arsenic model (Ayotte 2017): estimated share of 35,555 people on private wells in Walworth County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
Wisconsin DNR regulated sites: 508 regulated sites located in Walworth 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.