Mercer County Water Report

Mercer County earns a B grade for drinking water quality, scoring 62.3 out of 100. Over the past five years, EPA SDWIS records 15 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 large majority — 92.3% — of assessed waterways are impaired (12 of 13 water bodies) across Mercer County's watersheds. The leading impairment causes are pcbs in fish tissue and mercury in fish tissue. 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 2026-05-14T14:15:00.000-04:00) puts Delaware River at 11.0k cfs — near its historical average at 91% 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. Mercer County has extensive coverage with 158 active monitoring sites with 42,283 recent measurements on record. Predominant monitoring categories include physical 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.