State profile · EPA SDWIS + UCMR5
Wisconsin Drinking Water Quality
10,988 SDWIS-listed public water systems serve 5,131,439 people across Wisconsin. Violation rates use that full inventory; PFAS rates use only the UCMR5-tested subset.
- 10,988
- SDWIS water systems
- 285,161
- Total violations
- 72.1%
- SDWIS systems w/ a violation
- 25.2%
- UCMR5 PFAS rate (202 tested)
The verdict
72.1% of listed systems carry ≥1 SDWIS violation - lower-third rate (≤ 92.5%). According to EPA SDWIS population served, Wisconsin ranks #24 of 66 states and territories by people served through public water systems.
- #24 of 66
- Population · states corpus
- 285,161
- Total EPA violations on record
- 21%
- Health-based (MCL / treatment)
- 72.1%
- SDWIS systems with ≥1 violation
SDWIS violation % and UCMR5 PFAS % use different denominators (full inventory vs tested subset). Population ordinal uses SDWIS population served.
Wisconsin standing, low SDWIS violation-rate third
Wisconsin is in the lower third of jurisdictions by violation rate (72.1%; lower-third rate (≤ 92.5%)). That is a relative placement among peers, not a claim that most systems are clean - 7,923 of 10,988 still carry ≥1 record. Population served is mid-pack at 5,131,439 (mid served population (≤ 5,131,439)). Health-based share is 21% - a material slice is exposure-relevant, with the rest monitoring or reporting. UCMR5 PFAS detection is 25.2% on the tested subset (mid UCMR5 detection (≤ 35.3%)) - a different denominator from the SDWIS violation rate. Systems listed below are ranked by population served or violation count; pair rate with inventory size before reading exposure scale.
Nationwide similar states
Nearest by SDWIS violation rate
Nearest by population served
Health-based share of this violation record
EPA SDWIS classifications for Wisconsin's 285,161 recorded violations.
Wisconsin vs nearest violation-rate peers
Share of SDWIS-listed systems with at least one recorded violation; peers are nearest by absolute rate distance, not a fixed top-seven list.
- WI
Wisconsin
72.1 % of systems
- DE
Delaware
74.8 % of systems
- SC
South Carolina
65.3 % of systems
- MD
Maryland
79.9 % of systems
- HI
Hawaii
80.3 % of systems
What this shows Wisconsin's rate is 72.1% (7,923 of 10,988 systems; lower-third rate (≤ 92.5%)). This is a comparison of recorded SDWIS violations, not a measure of current water safety.
Wisconsin vs all jurisdictions by SDWIS system inventory
Where this state's public water system count sits among every state and territory on PlainWater
10,988 1st of 66 the highest of 66 jurisdictions
States and territories, banded by SDWIS-listed public water system count
Each bar is a band; taller bars hold more jurisdictions. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA SDWIS state aggregates · 2026-05-15
Largest Water Systems
Most Violations
Counties in Wisconsin
Showing top 30 of 71 counties.
Context: Check your water system · methodology · all states
Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.