Blue Earth County, Minnesota: drinking water report. Blue Earth County in southern Minnesota has about 68,000 residents, with Mankato as the county seat.
Blue Earth County in southern Minnesota has about 68,000 residents, with Mankato as the county seat. The city draws water from the Blue Earth River and deep groundwater wells. The county sits in the heart of Minnesota's corn and soybean belt, where intensive row crop agriculture dominates the landscape. Tile drainage systems designed to move water off fields quickly also move dissolved nitrate directly into waterways.
The Blue Earth River is one of the most nitrate-impaired rivers in Minnesota. According to the Minnesota Pollution Control Agency's 2024 water quality data, nitrate concentrations at the Mankato gauge averaged 11.4 mg/L during March-June – above the MCL of 10 mg/L. Tile drainage from surrounding agricultural fields delivers nitrate directly to streams without the benefit of soil filtration.
A 2024 University of Minnesota Extension study found that 19% of private wells tested in Blue Earth County exceeded the nitrate MCL. The concentration pattern correlates closely with tile-drained cropland, confirming the agricultural pathway. PFAS from the Mankato Regional Airport has been detected at 7 ppt in nearby monitoring wells.
Southern Minnesota's tile drainage infrastructure creates a direct pipeline from farm fields to waterways and aquifers. If you are on a private well in Blue Earth County, nitrate testing is not optional – nearly one in five wells exceeds the safe limit.
Check your water for the latest data. For nitrate, reverse osmosis is the most reliable household treatment. Our water filter guide ranks certified nitrate removal systems. Pull your detailed report for local data, and visit our Minnesota page for statewide context.