Collinsville Water Hardness & Quality Report (2026)

The Collinsville Water Department, operated by the City of Collinsville Public Works in Madison County, Illinois, serves approximately 25,000 residents. Water is sourced exclusively from multiple municipal groundwater wells, including Well #15 (currently on emergency status only). Raw well water undergoes filtration, disinfection, and chemical adjustment at the city's water plant before distribution. Recent actions include decommissioning contaminated wells to manage PFAS levels, with long-term upgrades planned by 2029 at an estimated $8 million cost, funded via grants, loans, and litigation against chemical producers.

The supply originates from the local groundwater aquifer within the Mahomet Bedrock Valley Aquifer system and associated glacial drift in southwestern Illinois. Paleozoic bedrock — primarily Pennsylvanian and Mississippian limestones, sandstones, and shales — has been fractured and dissolved over millennia. The hard supply character stems from prolonged contact with carbonate-rich formations like the Aux Vases Sandstone and Ste. Genevieve Limestone, which leach calcium and magnesium; no surface watershed influences dilute the chemistry, preserving the geological imprint.

Very hard water promotes extensive scale buildup in pipes, heaters, water heaters, dishwashers, washing machines, and coffee makers, insulating heating elements and clogging valves. Regular vinegar descaling, drain screen installation, and annual system flushing are advised. A whole-house water softener is strongly recommended given the extreme mineral load typical of Illinois groundwater. Recent PFAS detections prompted well removal — residents should use certified GAC or RO filters for drinking and cooking, though bathing remains safe. As of September 2024, finished water PFAS was reduced to safe levels via well adjustments per city notices.