Alton Water Hardness & Quality Report (2026)

Illinois American Water – Alton District serves the city of Alton and surrounding areas in Madison County, Illinois, providing drinking water to approximately 15,000 residents. The primary source is the Mississippi River, with raw water intake at the Alton Water Treatment Plant located near the riverfront. The utility treats river water through conventional processes including coagulation, sedimentation, filtration, and chlorine disinfection. Backup groundwater wells from local alluvial aquifers supplement supply if needed, though surface water dominates the distribution system.

The Mississippi River watershed upstream of Alton drains vast Midwestern terrain, with the Missouri River and Illinois River as key tributaries. Local geology features exposed Paleozoic carbonate rocks — notably Ordovician limestones and dolomites including the Galena and Maquoketa Groups — interspersed with Pleistocene glacial deposits. These formations release calcium and magnesium ions into the river through karst dissolution, while alluvial floodplain deposits amplify mineral content, producing a very hard supply at 293 mg/L.

At very hard levels (293 mg/L), scale buildup is severe, accelerating wear on water heaters, dishwashers, washing machines, and plumbing fixtures — reducing efficiency and lifespan by up to 50%. Soap lathers poorly, leaving spotted dishes and increasing detergent use. Regular vinegar cleaning of fixtures, installing scale-inhibiting filters, and annual water heater flushing are recommended. A water softener is strongly advised. The utility maintains pH around 8.5 using sodium hydroxide for corrosion control; iron is low at 0.0128 mg/L, and fluoride is added for dental health, with no MCL violations reported.