Dodge County, Wisconsin: drinking water report. Dodge County in south-central Wisconsin has about 89,000 residents in communities including Beaver Dam,…
Dodge County in south-central Wisconsin has about 89,000 residents in communities including Beaver Dam, Horicon, and Juneau. The county relies almost entirely on groundwater from glacial drift and shallow bedrock aquifers. Dairy farming is the economic backbone – the county's cattle density is among the highest in Wisconsin – and that agricultural intensity directly affects the aquifer beneath.
Nitrate contamination is widespread in Dodge County. According to the Wisconsin DNR's 2024 private well testing summary, 25% of tested wells exceeded the nitrate MCL of 10 mg/L – placing the county among the most nitrate-impacted in the state. Manure application from dairy operations and commercial fertilizer on row crops are the primary sources. The flat terrain and shallow water table provide minimal buffer.
Bacteria contamination accompanies the nitrate. A 2024 UW-Extension study found coliform bacteria in 16% of tested Dodge County wells, indicating surface water infiltration into the aquifer. The Horicon National Wildlife Refuge in the center of the county creates a unique hydrological feature – the Horicon Marsh influences groundwater flow patterns throughout the surrounding area.
One in four private wells in Dodge County exceeds the nitrate limit. If you have a well and have not tested it in the past year, the odds are not in your favor. Testing is inexpensive compared to the health consequences of chronic nitrate exposure.
Check your water for any available data. For nitrate at the concentrations found in this county, reverse osmosis is the recommended treatment. For bacteria, UV disinfection or shock chlorination addresses the microbial risk. Our water filter guide covers both. Get your detailed report for context, and visit our Wisconsin page for statewide patterns.