Prince William County Water Report

Prince William County earns an A grade for drinking water quality, scoring 70.6 out of 100. Over the past five years, EPA SDWIS records 3 health-based violations — a small cluster that warrants attention.

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 49.3% of assessed waterways are impaired (68 of 138 water bodies) across Prince William County's watersheds. The leading impairment causes are escherichia coli (e. coli) and pcbs 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 S F QUANTICO CREEK at 2.8 cfs — well below its long-term average at 40% 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. Prince William County has moderate coverage with 28 active monitoring sites with 13,089 recent measurements on record. Predominant monitoring categories include physical and nutrient. 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.