Miami Water Hardness & Quality Report (2026)

Miami's water is supplied by Miami-Dade Water and Sewer Department (WASD), drawing entirely from the Biscayne Aquifer — one of the most productive surficial aquifers in the United States and the sole source of drinking water for most of Miami-Dade County. The aquifer is accessed through a network of well fields across Miami-Dade County, with the largest being the Northwest Wellfield, Hialeah-Preston, and Alexander Orr Jr. Wellfield systems. The Alexander Orr Jr. Water Treatment Plant and the Hialeah and John E. Preston Water Treatment Plants treat groundwater before distribution. Miami-Dade's water system is one of the largest groundwater-based systems in the United States, serving over 2.3 million customers with no surface reservoir dependency.

Miami's moderate hardness of 137 mg/L is a product of the Biscayne Aquifer's unique geological character. The aquifer is contained within the Miami Limestone (Pleistocene age) and the underlying Fort Thompson Formation — porous, vuggy carbonate rocks formed from ancient coral reef and marine shell deposits laid down 125,000–500,000 years ago when sea level stood higher than today. Rainwater percolating through these highly porous limestone formations dissolves calcium carbonate at moderate rates, producing water of intermediate hardness typical of Florida coastal aquifer systems. The Biscayne Aquifer's shallow depth and high porosity also mean it is highly vulnerable to saltwater intrusion from Biscayne Bay, which WASD manages through careful well field operations.

Miami's moderately hard water is manageable in daily household use. White mineral deposits form gradually on showerheads and faucets, soap and detergent perform reasonably well, and glassware develops mild spotting over time without rinse-aid. The tropical climate means evaporation can concentrate minerals rapidly on outdoor fixtures and pool surrounds. Descaling showerheads and coffee machines every 2–3 months is standard practice, and dishwasher rinse-aid effectively eliminates glassware filming. A basic carbon-block filter also addresses any taste variation from the treatment process, which Miami residents occasionally notice during seasonal wellfield switching.