Pima County Water Report

Pima County's drinking water earned a C grade, scoring 53.4 out of 100. Over the past five years, EPA SDWIS records 128 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 13.3% of assessed waterways carry an impairment designation (6 of 45 water bodies) across Pima County's watersheds. The leading impairment causes are copper and ph. 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 2026-05-14T11:45:00.000-07:00) puts SANTA CRUZ RIVER at 34.5 cfs — running somewhat below its historical average at 82% of mean. 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. Pima County has extensive coverage with 632 active monitoring sites with 105,488 recent measurements on record. Predominant monitoring categories include organics, other and organics, pesticide. 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.