Riverside County Water Report

Riverside County earns a B grade for drinking water quality, scoring 65.1 out of 100. Over the past five years, EPA SDWIS records 87 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 notable 24.0% of assessed waterways carry an impairment designation (37 of 154 water bodies) across Riverside County's watersheds. The leading impairment causes are pathogens and nitrogen. 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 2026-05-14T11:30:00.000-07:00) puts COLORADO RIVER BELOW PALO VERDE DAM, AZ-CA at 7.3k cfs — near its historical average at 95% 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. Riverside County has extensive coverage with 247 active monitoring sites with 63,702 recent measurements on record. Predominant monitoring categories include organics, pesticide 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.