Aliso Viejo Water Hardness & Quality Report (2026)

Aliso Viejo, California, receives its water from the South Coast Water District (SCWD) and Irvine Ranch Water District (IRWD), serving southern Orange County. Primary sources are mixed: local groundwater from the Orange County Groundwater Basin (including San Joaquin Forearc aquifers), imported surface water via the Colorado River Aqueduct from Lake Mathews, and State Water Project supplies from the Sacramento–San Joaquin Delta. Water is treated at IRWD's facilities including the Michelson Water Treatment Plant and Foreman Water Treatment Plant, then blended and distributed through regional infrastructure.

The local supply draws from the Santa Ana River watershed and Orange County Groundwater Basin, underlain by Cenozoic sedimentary rocks including the Pleistocene San Pedro Formation (alluvial sands and gravels) and underlying Pliocene limestones and dolomites. Imported Colorado River water originates from Rocky Mountain snowmelt flowing through Paleozoic limestones such as the Kaibab and Redwall formations. State Water Project supplies come from granitic Sierra Nevada watersheds. This diverse geology imparts a hard supply character through mineral leaching from carbonate-rich formations in both groundwater aquifers and surface source rocks.

At moderately hard to hard levels, scale buildup occurs on fixtures and reduces efficiency in water heaters, dishwashers, washing machines, and pipes, leading to higher energy bills and shorter appliance life. Dry skin, soap scum, and spotting on dishes and glassware are common. Regular vinegar descaling of heaters and faucets, installing scale-inhibiting filters, and flushing systems annually are recommended. A water softener is advisable above moderately hard levels. IRWD's 2025 Water Quality Report confirms compliance with federal and state standards; no PFAS exceedances are reported. Treatment at IRWD plants includes coagulation, sedimentation, ozonation, filtration, UV disinfection, and chloramination.