Calumet County, Wisconsin: drinking water report. Calumet County on the eastern shore of Lake Winnebago has about 50,000 residents.
Calumet County on the eastern shore of Lake Winnebago has about 50,000 residents. Most communities rely on groundwater from the Silurian dolomite aquifer, with some systems purchasing water from neighboring Fox Valley utilities. The county's dairy industry – concentrated animal feeding operations and family farms alike – shapes the water quality beneath the thin soils that overlay the fractured bedrock.
Calumet County has one of the highest rates of nitrate-contaminated private wells in Wisconsin. According to the Wisconsin DNR's 2024 groundwater monitoring report, 29% of tested private wells in the county exceeded the nitrate MCL of 10 mg/L. The thin soil cover over fractured dolomite provides minimal filtration, allowing nitrate from manure spreading and fertilizer application to reach the aquifer rapidly.
Bacteria contamination compounds the problem. The same fractured bedrock that transmits nitrate also allows bacteria to enter wells. A 2024 UW-Extension study found that 18% of tested wells in Calumet County showed coliform bacteria, indicating surface water influence.
With nearly one in three private wells exceeding the nitrate limit, Calumet County well owners should treat testing as urgent rather than routine. Bacteria presence alongside nitrate suggests that your well casing may not be adequately sealed against surface infiltration.
Check your water for any available data. For nitrate, reverse osmosis at the kitchen tap is the most effective daily protection. For bacteria, UV disinfection or chlorination at the wellhead addresses the source. Our water filter guide covers both scenarios. Pull your detailed report for context, and visit our Wisconsin page for statewide data.