Well water in Portage County, Wisconsin

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Testing strongly recommended

private wells tested between 1988 and 2025 in Portage County had nitrate above the Wisconsin enforcement standard (10 mg/L), according to the UWSP Well Water Quality Viewer.

3,842 private wells tested 1988 to 2025 in state summaries; 5,095 test results across 12 contaminants from at least 136 wells, 1945 to 2024; nitrate has the most at 1,790. Data refreshed September 15, 2026.

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

An estimated 26,751 people in Portage County get their drinking water from a private well, per USGS 2015 county water use. That is about 38% of residents.

Separately, the USGS national arsenic model estimates that 4% of the 26,751 people on private wells in Portage County draw water above 10 ug/L (the model's range is 3% to 5%), 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, 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	Above state level	Wells tested	Highest	State level
Nitrate	21%	3,842	76	10 mg/L
Iron	19%	247	35,000	300 ug/L
Sodium	10%	219	162	20 mg/L
Total coliform	10%	1,284
E. coli	3%	122
Manganese	3%	307	7,977	300 ug/L
Lead	2%	279	96	15 ug/L
Chloride	1%	1,312	753	250 mg/L
Copper	1%	274	3.13	1.3 mg/L
Arsenic	<1%	422	11	10 ug/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Portage 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
Nitrate 1951 to 2024	27%	1,790	90%	3.9	208	10 mg/L EPA limit
Arsenic 1973 to 2024	<1%	160	71%	0.28	11	10 ug/L EPA limit
Fluoride 1945 to 2024	0%	393	90%	0.2	1	4 mg/L EPA limit
Lead 1973 to 2024	0%	138	71%	0	0.98	15 ug/L EPA limit
Copper 1976 to 2024	0%	86	71%	0	0.755	1.3 mg/L EPA limit
Uranium 1994 to 2024	0%	67	96%	1.37	8.16	30 ug/L EPA limit
Radium (226 + 228) 2003 to 2014	0%	18	72%	0.205	0.82	5 pCi/L EPA limit
Chloride 1945 to 2024	no limit	748	100%	4.6	430	250 mg/L nuisance level
Sodium 1951 to 2024	no limit	716	100%	2.1	33	20 mg/L health guideline
Iron 1945 to 2024	no limit	585	78%	50	38,000	300 ug/L nuisance level
Manganese 1945 to 2024	no limit	391	67%	1.54	3,200	300 ug/L health guideline

Sampled fewer than 10 times, too few to summarize: Radon (3).

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	26%1,580 samples	35%68 samples	28%130 samples	58%12 samples
Fluoride	0%296 samples	0%30 samples	0%61 samples	n/a
Arsenic	1%99 samples	0%10 samples	0%45 samples	n/a
Lead	0%77 samples	0%10 samples	0%45 samples	n/a
Copper	0%26 samples	0%10 samples	0%44 samples	n/a
Uranium	n/a	0%10 samples	0%45 samples	n/a

Nitrate above the limit in Portage County fell from 35% of 68 samples in the 2000s to 28% of 130 in the 2010s.

Fluoride, arsenic, lead, copper have held within a few points between the two most recent periods with enough samples.

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 Portage County who sent a sample to the state lab, the health-based limits most often exceeded were nitrate (21% of 3,842 wells), total coliform (10% of 1,284 wells), and E. coli (3% of 122 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 and sodium 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 Portage County

1
Nitrate
27% of 1,790 local samples were above the limit.
2
Total coliform
10% of 1,284 local wells tested were above the Wisconsin limit (any detection).
3
E. coli
3% of 122 local wells tested were above the Wisconsin limit (any detection).
4
Lead
2% of 279 local wells tested were above the Wisconsin enforcement standard.
5
Copper
1% of 274 local wells tested were above the Wisconsin enforcement standard.
6
Arsenic
<1% of 160 local samples were above the limit.
7
Radon
Median local reading is 260 pCi/L.
8
Iron
19% of 247 local wells tested were above the Wisconsin nuisance level.
9
Volatile organic compounds (VOCs)
163 leaking underground storage tank sites on record locally.

Test your Portage County well for nitrate, total coliform and E. coli

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 Portage County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

The rock under Portage County

Not a principal aquifer

The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.

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 Portage County

Wisconsin DNR records 163 leaking underground storage tank sites in Portage County, among 433 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.

163: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
37: lined landfills and transfer facilities
233: 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

Iron

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

Sodium

Point-of-use reverse osmosis; Distillation

Arsenic

Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange

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 nitrate

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

For nitrate

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 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 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.

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.

Free, no obligation

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

No water treatment company serves Portage 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 Portage County, and you get an email naming it first.

Common questions

Is there arsenic in well water in Portage County?

Arsenic was detected in 71% of 160 public well samples in Portage County, and <1% 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 Portage 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 Portage County

5 towns have fewer than 30 public samples and are included in the Portage County totals above rather than shown separately: Amherst village, Junction City village, Milladore village, Park Ridge village, Whiting village.

Counties near Portage 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: 5,095 samples in Portage 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 Portage County, up to 3,842 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 26,751 people on private wells in Portage 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: 433 regulated sites located in Portage 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.