Antioch Water Hardness & Quality Report (2026)

The City of Antioch provides drinking water to approximately 115,074 residents in Antioch, California, within Contra Costa County. Water is sourced from the Sacramento-San Joaquin River Delta, diverted by the Contra Costa Water District (CCWD) from four locations: Rock Slough near Oakley, Old River near Discovery Bay, Middle River on Victoria Island, and Mallard Slough in Bay Point. Conveyance occurs via the Contra Costa Canal, Los Vaqueros Pipeline, and Multi-Purpose Pipeline. Treatment at CCWD facilities involves conventional filtration, pre-oxidation with chlorine, and chloramine disinfection before distribution.

The Sacramento-San Joaquin Delta watershed spans the Central Valley, where river waters flow over Quaternary alluvium and Holocene deltaic sediments derived from Sierra Nevada erosion. Underlying formations include the Pleistocene-age Great Valley Sequence sands and clays, which release calcium and magnesium into the water through infiltration and runoff. Contributions from limestone and dolomite-bearing terrains upstream further influence the overall chemistry, imparting a moderately mineralised character to the supply through prolonged contact with mineral-rich Central Valley formations.

Moderately mineralised water promotes moderate scale buildup in water heaters, dishwashers, and coffee makers, reducing efficiency and increasing energy costs over time. Pipes and fixtures may accumulate deposits gradually; annual flushing of water heaters and regular deliming of affected appliances helps mitigate issues. A water softener is often recommended for households with noticeable spotting on dishes or reduced soap lathering to extend appliance life. Water quality earns a good rating (80/100), though two contaminants exceed EPA health-based guidelines; broader reports note seven such instances including chromium (hexavalent). The utility complies with lead and copper rules.