Waukesha County Water Report

Waukesha County's water systems carry a failing grade, scoring 19.5 out of 100. Over the past five years, EPA SDWIS records 340 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 small share — 7.6% — of assessed waterways are impaired (44 of 582 water bodies) across Waukesha County's watersheds. The leading impairment causes are phosphorus, total and total suspended solids (tss). 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 FOX RIVER at 99.3 cfs — running somewhat below its historical average at 85% 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. Waukesha County has extensive coverage with 187 active monitoring sites with 160,414 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.