Monroe County, Indiana: drinking water report. Monroe County in south-central Indiana has about 148,000 residents, including Bloomington and Indiana…
Monroe County in south-central Indiana has about 148,000 residents, including Bloomington and Indiana University. The City of Bloomington Utilities draws from Lake Monroe and Lake Griffy, supplemented by a wellfield. The county sits on limestone karst geology – the same type of terrain that created the region's famous caves and sinkholes – which creates unique water quality challenges.
Karst geology in Monroe County means surface contamination can reach groundwater rapidly through sinkholes and solution channels. According to the Indiana Geological and Water Survey's 2024 karst assessment, over 2,000 mapped sinkholes exist in Monroe County. Dye tracing studies have documented travel times from surface sinkholes to springs and wells of less than 72 hours.
Bloomington's surface water supply from Lake Monroe is well-protected, but private well users on the karst terrain face a different risk. A 2024 IDEM study found coliform bacteria in 22% of tested private wells in the county's karst zones. PFAS from the Monroe County Airport has been detected at 8 ppt in monitoring wells near the facility.
Monroe County's karst geology makes surface water protection critical – anything dumped on the ground near a sinkhole can end up in someone's well within days. Private well owners should never pour chemicals or waste near sinkholes, and testing for bacteria at least annually is essential.
Check your water for available data. For karst-influenced well water, UV disinfection handles bacteria, and reverse osmosis addresses PFAS and nitrate. Our water filter guide covers well water systems suited to karst terrain. Pull your detailed report for local data, and visit our Indiana page for statewide patterns.