Olmsted County, Minnesota: drinking water report. Olmsted County in southeastern Minnesota has a population of about 165,000, centered on Rochester – home
Olmsted County in southeastern Minnesota has a population of about 165,000, centered on Rochester – home to the Mayo Clinic. Rochester Public Utilities draws water exclusively from groundwater wells tapping the Prairie du Chien-Jordan and Mt. Simon-Hinckley aquifers. These deep carbonate and sandstone formations produce naturally hard water with a distinctive mineral profile. The county's karst geology, where limestone bedrock is dissolved into sinkholes and underground channels, creates direct pathways between the surface and the aquifer.
Karst vulnerability is the defining water quality concern in Olmsted County. According to the Minnesota Department of Health's 2024 groundwater assessment, 40% of the county is classified as having high or very high karst sensitivity, meaning surface contaminants can reach groundwater within hours or days of a spill or application event. Nitrate from agricultural fertilizers is the primary contaminant of concern – 15% of private wells tested in the county exceeded 5 mg/L, and 6% exceeded the MCL of 10 mg/L.
The EPA's UCMR5 data shows PFAS detections at low levels in the Rochester system. The Rochester International Airport has used AFFF firefighting foam, creating a localized PFAS concern. A 2024 MDH investigation documented PFAS in two monitoring wells near the airport at concentrations above Minnesota's health-based value of 15 ppt for PFOS.
Private well owners in Olmsted County should test for nitrate annually at minimum. The karst geology here means contamination can arrive at your well much faster than in areas with clay or thick soil overlying the aquifer.
Check your water for the latest public system data in your area. For nitrate, reverse osmosis or ion exchange filters are effective. For PFAS, reverse osmosis handles both. Our water filter guide covers well-water-specific systems. Pull your detailed report for trend data, and visit our Minnesota page for statewide patterns.