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Is Lake Koshkonong, WI tap water safe?

5 utilities serve Lake Koshkonong, by EPA’s records. Here is what EPA’s and Wisconsin’s records show for each, against the legal limits and the stricter health goals.

Matched to your utility using EPA records.

The short answer

2 of the 5 utilities serving Lake Koshkonong have a result above a legal limit or action level, or a health-based violation since 2016, in EPA’s and Wisconsin’s records: Edgerton Waterworks and Milton Waterworks.

Fort Atkinson Waterworks, which serves the most people here, has 2 results above the health goal. The worst: Lead at 13 ppb, above the health goal. Health goals are stricter than legal limits and are not enforced.

The water from Fort Atkinson Waterworks is very hard, typically 278 mg/L (16.2 grains per gallon). How Wisconsin’s water compares.

A town can be served by more than one utility, and some homes are on private wells. The name on your water bill tells you which is yours, and your ZIP code narrows it down. They are listed by how many people each serves in Lake Koshkonong’s ZIP codes, from EPA’s estimates.

What handles it

Each of these is certified, on a certifier’s listing, for a result above a line in Fort Atkinson Waterworks’s water, which serves the most people here. Another utility’s report names what handles its own results.

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Every claim, and more filters, in the full report

Water testing near Lake Koshkonong

A utility tests the water it sends out. A test of your own tap shows what your pipes add, and on a private well it is the only test there is. It takes a lab Wisconsin certifies.

The 3 labs Wisconsin certifies closest to Lake Koshkonong, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Rock County Health Department

    Janesville, WI · about 12 miles

    Certified for bacteria, nitrate

    (608) 757-5442

  • Janesville Wastewater Lab

    Janesville, WI · about 15 miles

    Certified for bacteria

    (608) 755-3120

  • Wisconsin Department of Agriculture, Trade and Consumer Protection

    Madison, WI · about 23 miles

    Certified for bacteria

    (608) 224-4821

Wisconsin State Laboratory of Hygiene: Well water test kits ordered by phone and shipped free; you pay to mail the sample back, and the lab bills you after testing. Tests run from bacteria alone to a homeowner package covering bacteria, nitrate, fluoride, metals, hardness, volatile organic compounds and atrazine. Bacteria is $35, nitrate $35, lead $38, and the homeowner package $450, as of July 1, 2026. Public Environmental and Water Testing Prices, Wisconsin State Laboratory of Hygiene.

All 156 certified labs for Wisconsin

ZIP codes in Lake Koshkonong

Which ZIP codes are in Lake Koshkonong: Census 2020 relationship files. Which utilities serve them, and how many people: EPA SDWIS and EPA’s service area map. Each utility’s results: EPA UCMR 5, EPA SDWIS, and EPA’s and the state’s compliance monitoring, as its report lists them. How they are measured: methodology. Certified labs: Wisconsin DNR and DATCP, certified and approved drinking water laboratories; distances from the Census 2020 ZIP code tabulation area gazetteer.

Near Lake Koshkonong

Other towns in Rock County with a page of their own.

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