EPA system WI1130224 · Wisconsin

Madison Water Utility: 2 PFAS found; PFHxS averaged 6.9 ppt, below the 10.0 ppt limit

System ID WI1130224; community water system; Wisconsin; source: groundwater; serves 272,000 people via 100,740 connections; status: active

In focus272,000people served, EPA registry

Public records. Clearer context.

Madison Water Utility is a local-government-owned community water system in Wisconsin serving about 272,000 people, matched to 20 ZIP codes.

PFAS treatment declared to EPA: None declared (40 of 40 sampling events) · PFAS found before UCMR 5: Yes, at 40 of 40 sampling events

PFAS and lithium: what EPA's national survey found

EPA tested this water for 30 substances and found 2.

Between October 2023 and October 2024, EPA's UCMR 5 program tested 1,200 samples from 20 sampling locations for 30 contaminants (29 PFAS plus lithium). 2 were detected above the reporting level in at least one sample.

Sampling-point average: mean of a location's two (ground water) or four (surface water) UCMR 5 results with non-detects counted as zero, EPA's method for comparing UCMR 5 data to the PFAS MCLs. EPA rounds to the reference value's significant digits before deciding whether an average is "greater than" an MCL (PFOA/PFOS averages count as above 4.0 ng/L only from 4.05 ng/L; lithium results count as above the 10 ppb reference only from 15 ppb). This site does not apply that rounding: "at or above" here means the measured value is numerically at or above the reference.

Utility-reported context (UCMR 5 questionnaire, aggregated across sampling events): PFAS previously found at this system: yes at 40 of 40 sampling events; potential PFAS sources nearby: yes at 40 of 40 sampling events; PFAS treatment in place: no PFAS treatment at 40 of 40 sampling events.

Lead at customer taps

In the latest completed monitoring period, ending Sep 30, 2023, 9 in 10 sampled homes had lead at or below 1.8 ppb, below the 15 ppb action level that triggers utility action. The action level has been reached in 3 of the 9 periods on record.

In the most recent completed lead monitoring period, ending Sep 30, 2023, the 90th-percentile lead result at customer taps was 1.8 ppb, below the action level of 15 ppb; 3 of the 9 monitoring periods on record reached the action level. The 90th percentile is the value that 9 in 10 sampled homes were at or below. Values are in parts per billion (ppb).

Drinking water violations since Sep 3, 2016

EPA lists 2 violations since Sep 3, 2016. 1 is health-based, meaning a contaminant or treatment rule was not met. The other 1 concerns missed monitoring, reporting or public notices. 1 is still open.

EPA's SDWIS database lists 2 violations recorded since Sep 3, 2016: 1 health-based (a contaminant above its maximum contaminant level, a disinfectant above its maximum residual level, or a required treatment technique not met), 1 other (public notification or consumer confidence report requirements); 1 is not yet resolved.

Sanitary surveys and site visits

Most recent state inspection: Apr 26, 2023 (sanitary survey); 1 visit since Sep 3, 2021.

What you can do about these results

ZIP codes served

Sources

Data vintage: EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Page generated 2026-09-03.

• EPA ECHO detailed facility report
• EPA UCMR 5 Data Finder
• EPA service-area boundary: modeled, 83.3 sq mi