PFAS Treatment as an Opportunity for Broader Drinking Water Improvements: Evidence from U.S. Water Systems

Installation of advanced filtration technologies for removing perfluoroalkyl and polyfluoroalkyl substances (PFAS) from drinking water presents an opportunity for considerable improvement in public drinking water quality. The U.S. Environmental Protection Agency’s drinking water standards published in 2024 for six PFAS were calculated to provide nationwide health benefits due to concurrent reduction in PFAS as well as total trihalomethanes (TTHMs or THM4), a group of carcinogenic disinfection byproducts. Here, we present a disinfection byproduct case study analysis of 19 community water systems that installed treatment to remove PFAS between 2018 and 2022. Fifteen case study systems observed reductions in THM4, and 15 observed reductions in haloacetic acids (HAA5) following the installation of PFAS treatment. Average reductions were 42% for THM4 (range: 9%–95%) and 50% for HAA5 (range: 2%–97%). Tap water served by 690 of the 1,083 systems with a single PFAS concentration exceeding the 2024 standards also contains co-occurring contaminants from four groups: disinfection byproducts, metals, nitrate/nitrite, and organic contaminants. Analysis of community water system treatment information and PFAS occurrence data from the U.S. EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR5) program suggests that a new regulatory framework based on treatment standards for multiple co-occurring contaminants would lead to a wide scope of potential health benefits due to simultaneous contaminant removal.