Williamson County Water Report

Williamson County's drinking water earned a C grade, scoring 62.0 out of 100. Over the past five years, EPA SDWIS records 13 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 35.5% of assessed waterways are impaired (50 of 141 water bodies) across Williamson County's watersheds. The leading impairment causes are sedimentation/siltation and alteration in stream-side or littoral vegetative covers. 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 2026-05-14T14:00:00.000-05:00) puts HARPETH RIVER BELOW FRANKLIN, TN at 43.1 cfs — well below its long-term average at 13% 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. Williamson County has extensive coverage with 76 active monitoring sites with 6,691 recent measurements on record. Predominant monitoring categories include physical and biological, counts. 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.