Ann Arbor Water Hardness & Quality Report (2026)

The City of Ann Arbor Water Treatment Plant supplies drinking water to approximately 120,000 residents in Ann Arbor and surrounding areas of Washtenaw County, Michigan. The primary source is surface water from the Huron River, specifically drawn at the intake of the Barton Plant on the Huron River. The utility operates a single advanced treatment facility featuring granular activated carbon (GAC) filtration, coagulation, sedimentation, and disinfection processes to meet all state and federal water quality standards for the community.

The Huron River watershed spans 919 square miles across 14 counties in Michigan, flowing through glacial landscapes overlying Paleozoic bedrock. Devonian-age carbonate formations — including limestones, dolomites, and shales such as the Antrim Shale and Bell Shale — dominate the geology, leaching minerals into the river system. Glacial till, sand, and gravel deposits of Washtenaw County further influence mineral content through surface runoff and river chemistry. This carbonate dissolution elevates calcium and magnesium, imparting a hard character to the supply alongside moderate bicarbonate alkalinity.

Hard water promotes scale buildup in pipes, water heaters, dishwashers, and washing machines — affected appliances may require 20–30% more energy for heating. Regular water heater flushing, scale-inhibiting filters, and vinegar descaling of fixtures help mitigate effects; a water softener is recommended to prevent spotting on dishes and glassware and improve soap efficiency. The supply maintains high pH around 9.3 (range 8.8–9.5) for corrosion control; GAC treatment has reduced PFAS (PFOA/PFOS) to below 10 ppt, well under advisory levels. Treatment includes lime softening, chlorination, and fluoride addition; no notable contaminants exceed MCLs.