Alameda County Water Report

Alameda County earns an A grade for drinking water quality, scoring 71.9 out of 100. Over the past five years, EPA SDWIS records 2 health-based violations — a small cluster that warrants attention.

Under the Clean Water Act §303(d), EPA ATTAINS tracks whether waterways meet quality standards for drinking, recreation, and aquatic life (reporting cycle: 2022). A substantial 30.9% of assessed waterways are impaired (29 of 94 water bodies) across Alameda County's watersheds. The leading impairment causes are mercury and trash. Impairment does not mean tap water is unsafe — it measures ambient waterway conditions upstream of treatment, not finished drinking water.

USGS NWIS gauge data (as of 2026-05-14T11:15:00.000-07:00) puts ALAMEDA C at 24.8 cfs — well below its long-term average at 22% of mean — low-flow conditions worth noting for water-dependent ecosystems. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Alameda County has extensive coverage with 53 active monitoring sites with 16,334 recent measurements on record. Predominant monitoring categories include microbiological and physical. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.