PFAS ("forever chemicals")
Hexafluoropropylene oxide dimer acid in U.S. tap water
91 public water systems across 21 U.S. states report Hexafluoropropylene oxide dimer acid in their annual Consumer Confidence Report. 5 sit at or above the federal limit.
See the PFAS Hotspots leaderboard → — every U.S. water system over EPA's finalized PFAS limit, ranked by severity, from the 2023–2025 UCMR5 lab dataset.
What it is
HFPO-DA ('GenX chemicals'), a newer-generation PFAS replacement compound.
Why it's regulated
Regulated by the EPA at 10 parts per trillion and included in the PFAS Hazard Index.
At or above the federal limit (5)
| Water system | Measured | vs. limit |
|---|---|---|
| Backbone Mountain Boys Camp, MD 2024 annual report | 10 ng/L | 1.0× the limit |
| Campus Hills, MD 2024 annual report | 10 ng/L | 1.0× the limit |
| Cheltenham Youth Facility, MD 2024 annual report | 10 ng/L | 1.0× the limit |
| Eastern Correctional Institute, MD 2024 annual report | 10 ng/L | 1.0× the limit |
| Town of Accident, MD 2024 annual report | 10 ng/L | 1.0× the limit |
Approaching the limit (1)
| Water system | Measured | vs. limit |
|---|---|---|
| Columbia, SC 2024 annual report | 8.7 ng/L | 0.9× the limit |
Within the federal limit (84)
| Water system | Measured |
|---|---|
| New Orleans, LA 2024 annual report | 0–5.4 ng/L |
| Mendota, City of — Mendota, Ca, CA 2023 annual report | 0–5 ng/L |
| Charleston, SC 2024 annual report | 2.3 ng/L |
| Cincinnati, OH 2024 annual report | 1 ng/L |
| Fayetteville, NC 2024 annual report | 1 ng/L |
| Thornton, CO 2024 annual report | 0.1–0.3 ng/L |
| City of Baltimore, MD 2024 annual report | 0.25 ng/L |
| Columbus, GA 2024 annual report | 0.18 ng/L |
| Wilmington, NC 2024 annual report | 0.09 ng/L |
| Tempe, AZ 2024 annual report | 0.01 ng/L |
| Lynwood-city, Water Dept. — Lynwood, Ca, CA 2023 annual report | 0.0009 ng/L |
| Albuquerque, NM 2024 annual report | Not detected ng/L |
| Anchorage, AK 2024 annual report | Not detected ng/L |
| Bellflower Municipal Water System — Rosemead, Ca, CA 2023 annual report | Not detected ng/L |
| Boonsboro Keedysville, MD 2024 annual report | Not detected ng/L |
| Brown Deer, WI 2023 annual report | Not detected ng/L |
| Butler, WI 2023 annual report | Not detected ng/L |
| Cal American Water Co — Rosemead, Ca, CA 2023 annual report | Not detected ng/L |
| Cal-am Water Company - Duarte — Rosemead, Ca, CA 2023 annual report | Not detected ng/L |
| Cal/am Water Company - Baldwin Hills — Rosemead, Ca, CA 2023 annual report | Not detected ng/L |
| Calvert Manor, MD 2024 annual report | Not detected ng/L |
| Carpinteria Valley Water District — Carpinteria, Ca, CA 2023 annual report | Not detected ng/L |
| Cary, NC 2025 annual report | Not detected ng/L |
| Chandler, AZ 2024 annual report | 0 ng/L |
| Chesapeake, VA 2023 annual report | Not detected ng/L |
| City of Mountain House — Mountain House, Ca, CA 2023 annual report | Not detected ng/L |
| City of Pleasanton — Pleasanton, Ca, CA 2023 annual report | Not detected ng/L |
| Cotati, City of — Cotati, Ca, CA 2023 annual report | Not detected ng/L |
| Dallas, TX 2024 annual report | Not detected ng/L |
| Dearborn, MI 2024 annual report | Not detected ng/L |
| East Valley Water District — Highland, Ca, CA 2023 annual report | Not detected ng/L |
| El Cajon, CA 2024 annual report | Not detected ng/L |
| Fallbrook Pud — Fallbrook, Ca, CA 2023 annual report | Not detected ng/L |
| Fillmore Water Dept — Fillmore, Ca, CA 2023 annual report | Not detected ng/L |
| Foothill Municipal Water Dist. — La Canada Flintridge, Ca, CA 2023 annual report | Not detected ng/L |
| Franklin, WI 2023 annual report | Not detected ng/L |
| Glendale, AZ 2024 annual report | Not detected ng/L |
| Grand Rapids, MI 2025 annual report | Not detected ng/L |
| Greendale, WI 2023 annual report | Not detected ng/L |
| Greenfield, WI 2023 annual report | Not detected ng/L |
| Hales Corners, WI 2023 annual report | Not detected ng/L |
| Helix Water District — La Mesa, Ca, CA 2023 annual report | Not detected ng/L |
| Lakewood, NJ 2025 annual report | 0 ng/L |
| Lexington, KY 2024 annual report | Not detected ng/L |
| Los Angeles Cwwd 36-val Verde — Alhambra, Ca, CA 2023 annual report | Not detected ng/L |
| Louisville, KY 2024 annual report | 0 ng/L |
| Lubbock, TX 2024 annual report | Not detected ng/L |
| Menomonee Falls, WI 2023 annual report | Not detected ng/L |
| Mequon, WI 2023 annual report | Not detected ng/L |
| Milwaukee, WI 2023 annual report | Not detected ng/L |
Showing 50 of 84. The full list is in the JSON API.
Frequently asked
+What is Hexafluoropropylene oxide dimer acid?
HFPO-DA ('GenX chemicals'), a newer-generation PFAS replacement compound. Regulated by the EPA at 10 parts per trillion and included in the PFAS Hazard Index.
+What is the federal limit for Hexafluoropropylene oxide dimer acid in drinking water?
The federal MCL for Hexafluoropropylene oxide dimer acid is 10 ng/L. The EPA enforces this against the regulated reporting statistic (typically a running annual average or 90th percentile), not a single-sample spike.
+How many U.S. water systems have Hexafluoropropylene oxide dimer acid over the federal limit?
5 of the 91 public water systems on The Water Map report Hexafluoropropylene oxide dimer acid at or above its federal limit, spanning 21 U.S. states. The full list is on this page.
+How can I check if Hexafluoropropylene oxide dimer acid is in my city's tap water?
Search your city on The Water Map (https://www.thewatermap.com/) or browse the list on this page. Every U.S. public water utility is required to publish an annual Consumer Confidence Report that lists every contaminant it measured, including Hexafluoropropylene oxide dimer acid.
See Hexafluoropropylene oxide dimer acid on the map
Color-coded by status across the whole country.
Open the map →