St. Louis Water Hardness & Quality Report (2026)

The City of St. Louis Water Division supplies drinking water to approximately 140,000 customers across 62 square miles in St. Louis City and parts of St. Louis County. Water sources are the Missouri River, treated at the Howard Bend Plant (capacity up to 300 million gallons per day), and the Mississippi River (predominantly Missouri River water), treated at the Chain of Rocks Plant (average 112 million gallons per day combined). American Water also serves adjacent St. Louis County and St. Charles County, sourcing from the Missouri and Meramec Rivers with a daily supply of 180 million gallons. Both utilities employ conventional treatment including coagulation, sedimentation, filtration, and disinfection.

The watershed encompasses the upper Missouri River basin, draining from the Rocky Mountains through the Great Plains into Missouri, with key tributaries including the Osage and Gasconade Rivers. Underlying geology features Paleozoic sedimentary rocks, notably Mississippian-age limestones and dolomites in the Ozarks, which dissolve to impart minerals. The river picks up calcium and magnesium ions from limestone aquifers and loess soils, yielding a hard-character supply through natural geological dissolution rather than deep groundwater extraction.

Moderate hardness causes scale buildup on fixtures, reducing efficiency in water heaters, dishwashers, washing machines, boilers, and coffee makers — limescale can shorten appliance lifespan by 20–30%. Regular descaling with vinegar, drain screens, and high-efficiency detergents help mitigate effects. A water softener is often recommended for households noticing spotting on dishes or dry skin. Water quality exceeds EPA and Missouri DNR standards; lead 90th percentile is 0.001 µg/L; fluoride is adjusted to 0.6 mg/L; no PFAS exceedances in recent CCRs; over 150 contaminants are continuously monitored.