Wisconsin PFAS results from EPA's final data
Report published Nov 14, 2026 · EPA UCMR 5 final data file of Oct 15, 2026 (samples collected 2023–2025) · Method · National results →
18 Wisconsin water systems serving 184,985 people had PFAS above a 2024 federal limit in EPA's final round of nationwide PFAS testing: 9% of the 196 Wisconsin systems tested, compared with 11% nationally.
Highest PFOA or PFOS averages in Wisconsin
- Saukville Waterworks Saukville · PFOS30.5 ppt
- Prairie du Chien Waterworks Prairie du Chien · PFOS25 ppt
- Tomahawk Waterworks Tomahawk · PFOA20 ppt
- Kewaskum Waterworks Kewaskum · PFOA13.5 ppt
- Marshfield Utilities Marshfield · PFOS13 ppt
- Weston Municipal Utilities Weston · PFOS10.8 ppt
- Prescott Waterworks Prescott · PFOA9.4 ppt
- Rib Mountain Water Utility Wausau · PFOS8.5 ppt
- Hartford Waterworks Hartford · PFOA6.5 ppt
- Rhinelander Water & Wastewater Rhinelander · PFOA6.15 ppt
- Pewaukee City Water and Sewer Utility Pewaukee · PFOS6 ppt
- Palmyra Waterworks Palmyra · PFOS5.2 ppt
- La Crosse Waterworks La Crosse · PFOS4.9 ppt
- Lake Geneva Utility Commission Lake Geneva · PFOA4.5 ppt
- Hartland Waterworks Hartland · PFOA4.4 ppt
Chart data as a table
| System | ppt |
|---|---|
| Saukville Waterworks · Saukville · PFOS | 30.5 |
| Prairie du Chien Waterworks · Prairie du Chien · PFOS | 25 |
| Tomahawk Waterworks · Tomahawk · PFOA | 20 |
| Kewaskum Waterworks · Kewaskum · PFOA | 13.5 |
| Marshfield Utilities · Marshfield · PFOS | 13 |
| Weston Municipal Utilities · Weston · PFOS | 10.8 |
| Prescott Waterworks · Prescott · PFOA | 9.4 |
| Rib Mountain Water Utility · Wausau · PFOS | 8.5 |
| Hartford Waterworks · Hartford · PFOA | 6.5 |
| Rhinelander Water & Wastewater · Rhinelander · PFOA | 6.15 |
| Pewaukee City Water and Sewer Utility · Pewaukee · PFOS | 6 |
| Palmyra Waterworks · Palmyra · PFOS | 5.2 |
| La Crosse Waterworks · La Crosse · PFOS | 4.9 |
| Lake Geneva Utility Commission · Lake Geneva · PFOA | 4.5 |
| Hartland Waterworks · Hartland · PFOA | 4.4 |
Largest systems above a limit
| # | System | People served |
|---|---|---|
| 1 | La Crosse Waterworks La Crosse Above: PFOA, PFOS | 53,000 |
| 2 | Marshfield Utilities Marshfield Above: PFOS | 18,815 |
| 3 | Weston Municipal Utilities Weston Above: PFOA, PFOS | 16,000 |
| 4 | Hartford Waterworks Hartford Above: PFOA, PFOS | 15,805 |
| 5 | Sturgeon Bay Waterworks Sturgeon Bay Above: PFOS | 9,700 |
| 6 | Hartland Waterworks Hartland Above: PFOA, PFOS | 9,212 |
| 7 | Pewaukee City Water and Sewer Utility Pewaukee Above: PFOA, PFOS, PFHxS, Hazard Index | 8,671 |
| 8 | Rhinelander Water & Wastewater Rhinelander Above: PFOA | 8,234 |
| 9 | Lake Geneva Utility Commission Lake Geneva Above: PFOA | 7,107 |
| 10 | Rib Mountain Water Utility Wausau Above: PFOA, PFOS | 6,398 |
All 18 Wisconsin systems above a limit
Every Wisconsin community water system whose UCMR 5 results averaged above a 2024 federal PFAS limit, largest first. Systems that were not tested are not listed: not tested is not the same as not detected.
Full list: 18 systems, largest first
| System | People served |
|---|---|
| La Crosse Waterworks La Crosse Above: PFOA, PFOS | 53,000 |
| Marshfield Utilities Marshfield Above: PFOS | 18,815 |
| Weston Municipal Utilities Weston Above: PFOA, PFOS | 16,000 |
| Hartford Waterworks Hartford Above: PFOA, PFOS | 15,805 |
| Sturgeon Bay Waterworks Sturgeon Bay Above: PFOS | 9,700 |
| Hartland Waterworks Hartland Above: PFOA, PFOS | 9,212 |
| Pewaukee City Water and Sewer Utility Pewaukee Above: PFOA, PFOS, PFHxS, Hazard Index | 8,671 |
| Rhinelander Water & Wastewater Rhinelander Above: PFOA | 8,234 |
| Lake Geneva Utility Commission Lake Geneva Above: PFOA | 7,107 |
| Rib Mountain Water Utility Wausau Above: PFOA, PFOS | 6,398 |
| Waupaca Waterworks Waupaca Above: PFOS | 6,062 |
| Prairie du Chien Waterworks Prairie du Chien Above: PFOS | 6,005 |
| Kewaskum Waterworks Kewaskum Above: PFOA | 4,309 |
| Saukville Waterworks Saukville Above: PFOS, PFHxS, Hazard Index | 4,268 |
| Prescott Waterworks Prescott Above: PFOA, PFHxS, Hazard Index | 4,258 |
| Tomahawk Waterworks Tomahawk Above: PFOA | 3,180 |
| Schofield Waterworks Schofield Above: PFOA | 2,205 |
| Palmyra Waterworks Palmyra Above: PFOS | 1,756 |
The same list, with PFOA and PFOS averages, is in the data download.
Which limits were exceeded
| PFAS | Federal limit | Systems above it |
|---|---|---|
| PFOA 138,379 people | 4 ppt | 12 |
| PFOS 155,692 people | 4 ppt | 12 |
| PFHxS 17,197 people | 10 ppt | 3 |
| PFNA | 10 ppt | 0 |
| GenX (HFPO-DA) | 10 ppt | 0 |
| Hazard Index 17,197 people | 1 | 3 |
"–" in the table above means not detected. A system can be above more than one limit. EPA proposed in May 2026 to rescind the PFHxS, PFNA, GenX and Hazard Index limits. That proposal is not final.
Wisconsin has its own PFAS rules. NR 809.221 Table Da (CR 25-068) adds Hazard Index MCL of 1 (HFPO-DA, PFBS, PFHxS, PFNA). MCL compliance by 2029-04-26. Replaced 2022 state PFOA/PFOS MCL. Details. This report compares results with the federal limits only.
Data and how to cite it
- Download every Wisconsin water system as CSV (PFOA and PFOS averages, systems above a limit, lead, violations).
- EPA's source file: UCMR 5 occurrence data.
Suggested citation:
Tap Water Results, "Wisconsin PFAS results from EPA's final UCMR 5 data" (published Nov 14, 2026, EPA data file of Oct 15, 2026). https://tapwaterresults.com/pfas/wisconsin/
You're welcome to quote and republish these figures with a link back. Questions from reporters: see contact.
Method
For each system we average each entry point's UCMR 5 results (non-detects count as zero, complete sets of samples only) and compare the highest entry-point average with the 2024 federal limit, using EPA's rounding. This is how EPA compares UCMR 5 results to the limits in its own data summary, and our national counts match EPA's published table within 2% (how we check). Results are monitoring data from 2023–2025, not compliance determinations, and treatment installed since then is not reflected. Full method.
Questions
How many Wisconsin water systems have PFAS above the limit?
18 of the 196 Wisconsin community water systems EPA tested in 2023–2025 (9%) had at least one entry-point average above a 2024 federal PFAS limit. They serve 184,985 people. Nationally the share is 11%.
Are these systems violating the law?
Not yet. Systems have until 2029 to meet the 2024 limits, and EPA has proposed moving the PFOA and PFOS deadline to 2031 and rescinding the other limits. EPA's UCMR 5 results are monitoring data and do not determine compliance.
Which systems were tested?
EPA's UCMR 5 tested every community water system serving more than 3,300 people and a representative sample of smaller ones. Systems that were not tested have no federal result, which is not the same as having no PFAS.
All Wisconsin water systems → · National results → · PFAS results for every state →
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.