Hercules Water Hardness & Quality Report (2026)

The East Bay Municipal Utility District (EBMUD) provides water to Hercules, California, serving over 1.4 million people across Contra Costa and Alameda counties. The primary source is the Mokelumne River via the Mokelumne Aqueduct, with storage in Pardee Reservoir and local reservoirs including Upper San Leandro and Lafayette. Treatment occurs at the EBMUD Jones Water Treatment Plant and supplemental facilities, delivering treated surface water to Hercules residents. No local groundwater is reported in the supply mix; treatment employs coagulation with polymers, flocculation, sedimentation, ozonation, filtration, chloramination, and fluoride addition.

The Mokelumne River watershed spans the Sierra Nevada, flowing through Mesozoic granitic batholiths and metavolcanic rocks of Jurassic-Cretaceous age, entering softer alluvial and sedimentary layers in the Great Valley. EBMUD's intake at Pardee Reservoir captures snowmelt-influenced water shaped by these geologies, which impart a moderately mineralised character through natural dissolution of calcium- and magnesium-bearing minerals from felsic rocks and downstream sediments. This geology yields a supply with moderate mineral content, distinct from softer coastal or harder groundwater-dominated areas.

Moderately hard water in Hercules can lead to noticeable scale buildup in appliances like water heaters, dishwashers, and coffee makers, reducing efficiency over time and increasing energy costs. Soap lathering is reduced, leaving films on skin, hair, and laundry. Maintenance tips include regular vinegar descaling of fixtures, installing sediment filters on faucets, and using rinse aids in dishwashers. A water softener is often recommended for households experiencing these effects. EBMUD water meets all EPA MCLGs with zero violations across 147+ contaminants tested; no PFAS exceedances are reported, and pH is typically 8.5–9.5 post-treatment for corrosion control.