Redwood City Water Hardness & Quality Report (2026)

Redwood City, California, the San Mateo County seat on San Francisco Bay, draws its municipal water supply through the City of Redwood City Water Division, sourcing from the Bay Area Water Supply and Conservation Agency (BAWSCA) — receiving treated Hetch Hetchy Aqueduct water from the San Francisco Public Utilities Commission (SFPUC) and supplemental storage from Crystal Springs Reservoir (San Mateo County). Hetch Hetchy Aqueduct water originates from the Tuolumne River in Yosemite National Park. Water hardness in Redwood City measures 178 mg/L — classified as hard, unexpectedly high for a Hetch Hetchy–sourced city.

Redwood City's hard supply — strikingly higher than San Francisco (75 mg/L) on the same SFPUC Hetch Hetchy source — indicates a significant local groundwater or non-SFPUC supply fraction blended in the Redwood City distribution. The Redwood City service area overlies the San Francisco Bay Estuary plain — where local groundwater from the San Francisco Bay alluvial plain and the Santa Cruz Mountains Franciscan Complex drainage could contribute substantially harder water through local wells or distribution blending. Crystal Springs Reservoir contributions from local Santa Cruz Mountains watershed may also add moderate mineral content. The dramatically higher reading than San Francisco proper suggests Redwood City draws a significant fraction of its supply from local sources beyond the SFPUC aqueduct.

At 178 mg/L, Redwood City residents face regular hard water challenges. Scale deposits form on faucet aerators, showerheads, and appliances within weeks — monthly descaling with citric acid solution is standard maintenance. Dishwashers require rinse-aid, and water heaters benefit from annual inspection. City of Redwood City Water Division and SFPUC consistently deliver water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.