This USGS research marks the first time anyone has tested for and compared PFAS in tap water from both private and government-regulated public water supplies on a broad scale throughout the country. Those data were used to model and estimate PFAS contamination nationwide. This USGS study can help members of the public to understand their risk of exposure and inform policy and management decisions regarding testing and treatment options for drinking water. 

PFAS are a group of synthetic chemicals used in a wide variety of common applications, from the linings of fast-food boxes and non-stick cookware to fire-fighting foams and other purposes. High concentrations of some PFAS may lead to adverse health risks in people, according to the U.S. Environmental Protection Agency. Research is still ongoing to better understand the potential health effects of PFAS exposure over long periods of time. Because they break down very slowly, PFAS are commonly called “forever chemicals.” Their persistence in the environment and prevalence across the country make them a unique water-quality concern. 

A scientist wearing black gloves is collecting a sample of tap water from the kitchen sink using small plastic vials. 

"USGS scientists tested water collected directly from people’s kitchen sinks across the nation, providing the most comprehensive study to date on PFAS in tap water from both private wells and public supplies,” said USGS research hydrologist Kelly Smalling, the study’s lead author. “The study estimates that at least one type of PFAS – of those that were monitored – could be present in nearly half of the tap water in the U.S. Furthermore, PFAS concentrations were similar between public supplies and private wells.”  

The EPA regulates public water supplies, and homeowners are responsible for the maintenance, testing and treatment of private water supplies. Those interested in testing and treating private wells should contact their local and state officials for guidance. Testing is the only way to confirm the presence of these contaminants in wells. For more information about PFAS regulations, visit the EPA’s website on addressing PFAS. 

The study tested for 32 individual PFAS compounds using a method developed by the USGS National Water Quality Laboratory. The most frequently detected compounds in this study were PFBS, PFHxS and PFOA. The interim health advisories released by the EPA in 2022 for PFOS and PFOA were exceeded in every sample in which they were detected in this study. 

Scientists collected tap water samples from 716 locations representing a range of low, medium and high human-impacted areas. The low category includes protected lands; medium includes residential and rural areas with no known PFAS sources; and high includes urban areas and locations with reported PFAS sources such as industry or waste sites.  

This USGS map shows the number of PFAS detected in tap water samples from select sites across the nation. The findings are based on a USGS study of samples taken between 2016 and 2021 from private and public supplies at 716 locations. The map does not represent the only locations in the U.S. with PFAS.  

Most of the exposure was observed near urban areas and potential PFAS sources. This included the Great Plains, Great Lakes, Eastern Seaboard, and Central/Southern California regions. The study’s results are in line with previous research concluding that people in urban areas have a higher likelihood of PFAS exposure. USGS scientists estimate that the probability of PFAS not being observed in tap water is about 75% in rural areas and around 25% in urban areas.  

Learn more about USGS research on PFAS by reading the USGS strategy for the study of PFAS and visiting the PFAS Integrated Science Team’s website. The new study builds upon previous research by the USGS and partners regarding human-derived contaminants, including PFAS, in drinking water and PFAS in groundwater.