San Juan County Water Report

San Juan County's water systems carry a failing grade, scoring 24.3 out of 100. Over the past five years, EPA SDWIS records 96 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 25.7% of assessed waterways carry an impairment designation (18 of 70 water bodies) across San Juan County's watersheds. The leading impairment causes are escherichia coli (e. coli) and temperature. 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 2026-05-14T13:00:00.000-06:00) puts SAN JUAN RIVER at 951.0 cfs — well below its long-term average at 50% 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. San Juan County has extensive coverage with 119 active monitoring sites with 67,293 recent measurements on record. Predominant monitoring categories include inorganics, minor, metals 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.