Orinda Water Hardness & Quality Report (2026)

Orinda, California, in Contra Costa County — a Contra Costa County city in the Lamorinda hills corridor adjacent to Lafayette and Moraga, one of the affluent East Bay hill communities in the Oakland-Berkeley Hills suburban belt — receives its municipal water from the East Bay Municipal Utility District (EBMUD), drawing from the Mokelumne River at Pardee Reservoir (Amador County, Sierra Nevada foothills) through the EBMUD Mokelumne Aqueduct system.

The very soft 51 mg/L hardness and low TDS of 110.9 mg/L reflect EBMUD's characteristically soft Sierra Nevada Mokelumne supply. The Mokelumne River rises in the Sierra Nevada (Cretaceous Sierra Nevada Batholith granite and metamorphic roof pendant) — primarily insoluble silicate rock — producing very soft water. EBMUD's supply is one of the softest large metropolitan supplies in California, and Orinda receives the same EBMUD Mokelumne water as the broader East Bay system (Oakland, Berkeley, Walnut Creek), all characterized by the 40-80 mg/L hardness range.

At 51 mg/L, Orinda's water is very soft — essentially no scale forms, soap lathers abundantly, and appliances maintain maximum efficiency. Annual descaling is more than sufficient. The PFAS level of 3.5 ppt warrants a certified drinking water filter — the Concord Naval Weapons Station (Contra Costa County — documented AFFF legacy on the Sacramento-San Joaquin Delta watershed), the Lawrence Berkeley National Laboratory (East Bay hills), and the San Francisco Bay Area industrial-military PFAS background contribute to Orinda's readings.