Contaminant · PFAS
4:2 FTS in drinking water
1H,1H,2H,2H-perfluorohexane sulfonic acid, a fluorotelomer sulfonate.
Data as of EPA UCMR 5 final release, August 2026 (file dated Aug 28, 2026) · EPA SDWIS 2026Q2 (file dated Jul 9, 2026). How we build these pages
What the rules say
4:2 FTS has no federal limit or EPA health reference value.
Read the EPA source for 4:2 FTS.
Across the country
EPA tested 10,307 water systems for 4:2 FTS and found it in 3. Half of the systems that found it measured less than 3.2 ppt, and one in ten measured more than 6.7 ppt.
EPA's final UCMR 5 occurrence file contains 66,361 4:2 FTS results from 10,307 systems. 3 results were at or above the minimum reporting level, across 3 systems. Among detections, the median was 3.2 ppt and the 90th percentile was 6.7 ppt.
Systems with the highest recorded 4:2 FTS results
| System | State | Population served | Recorded value | Records / periods |
|---|---|---|---|---|
| Emerald Coast Utilities Authority (Ecua) FL1170525 | Florida | 242,172 | 7.6 ppt | 1 |
| Sauk IL0312790 | Illinois | 9,921 | 3.2 ppt | 1 |
| Canton Water Dept MA4050000 | Massachusetts | 22,766 | 3.0 ppt | 1 |
Filters and testing
NSF/ANSI 58 (reverse osmosis)
A standard number by itself is not a contaminant claim. Check the product's current certification listing and performance data sheet for 4:2 FTS or the specific contaminant you want to reduce. A utility-level record is not a test of your own faucet.