Orange County Water Report

Orange County earns an A grade for drinking water quality, scoring 71.5 out of 100. Over the past five years, EPA SDWIS records 8 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 40.0% of assessed waterways are impaired (84 of 210 water bodies) across Orange County's watersheds. The leading impairment causes are pathogens and toxicity. 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 2026-05-14T12:00:00.000-07:00) puts SANTA ANA R A SANTA ANA CA at 0.0 cfs — well below its long-term average at 0% 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. Orange County has extensive coverage with 216 active monitoring sites with 127,039 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.