Ventura County Water Report

Ventura County earns a B grade for drinking water quality, scoring 63.0 out of 100. Over the past five years, EPA SDWIS records 41 health-based violations — a pattern that public water utilities are required to disclose and correct.

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 43.7% of assessed waterways are impaired (80 of 183 water bodies) across Ventura County's watersheds. The leading impairment causes are pathogens 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 SANTA CLARA R at 76.5 cfs — near its historical average at 107% of mean flow. 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. Ventura County has extensive coverage with 72 active monitoring sites with 24,665 recent measurements on record. Predominant monitoring categories include microbiological and organics, other. 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.