PFAS get into water mainly through six pathways: industrial discharge from factories that make or use them, aqueous film-forming firefighting foam (AFFF) at military bases and airports, leachate draining out of landfills, treated wastewater and land-applied biosolids from sewage plants, atmospheric deposition that rains PFAS back down, and the slow breakdown of everyday consumer products. PFAS are a family of thousands of human-made chemicals often called “forever chemicals” because they resist breaking down. Once released, they move easily through soil into groundwater and travel long distances in rivers, which is why they turn up in tap water far from any obvious source.
Key takeaways
– Industrial discharge and firefighting foam are the two most concentrated sources, but landfills, wastewater, biosolids, and air spread PFAS everywhere else.
– The U.S. Geological Survey estimated in 2023 that at least 45% of the nation’s tap water contains one or more PFAS.
– PFAS are both persistent and highly mobile in water, so contamination often travels far from where it started.
Why PFAS end up in water in the first place
PFAS stands for per- and polyfluoroalkyl substances, a group of more than 12,000 synthetic chemicals built around one of the strongest bonds in chemistry: the bond between carbon and fluorine. That bond is what makes PFAS useful for repelling water, grease, and stains, and it is also what makes them so hard to get rid of. The U.S. Environmental Protection Agency (EPA) describes PFAS as chemicals that “break down very slowly and can build up in people, animals, and the environment over time.” This is the reason for the nickname “forever chemicals.”
Two properties explain why so much PFAS ends up in water. First, they are persistent, meaning they do not naturally degrade the way many pollutants do. Second, many of the most common PFAS are mobile, meaning they dissolve readily and do not stick tightly to soil. When PFAS reach the ground, they move down into groundwater and outward into streams instead of staying put. That combination lets a single release keep contaminating water supplies for decades and travel to wells and rivers well beyond the original site.
To see how widespread this is, consider a 2023 study by the U.S. Geological Survey (USGS). Scientists collected tap water directly from kitchen taps at 716 locations across the country between 2016 and 2021, sampling both private wells and public water systems. They estimated that at least 45% of the nation’s tap water contains one or more types of PFAS. Because the study tested for only 32 of the thousands of known PFAS, the researchers noted that the true figure is likely higher.
The six main pathways PFAS take into water
The table below summarizes the major routes. The sections that follow explain each one in plain terms.
| Source | How it reaches water | Example |
|---|---|---|
| Industrial discharge | Factories release PFAS in wastewater or air; it enters rivers and groundwater | Chemical plants, chrome plating, electronics and textile makers |
| Firefighting foam (AFFF) | Foam soaks into soil during use or training, then seeps into groundwater | Military bases, airports, fire training grounds |
| Landfill leachate | Rain filters through PFAS-containing waste, creating contaminated liquid | Municipal and industrial landfills |
| Wastewater and biosolids | Treatment plants cannot remove PFAS; it leaves in treated water or sludge spread on farmland | Sewage plant effluent, fertilizer from treated sludge |
| Atmospheric deposition | PFAS released into the air settle onto land and water in rain and dust | Emissions from manufacturing facilities |
| Consumer product breakdown | Treated products shed PFAS during use and disposal, washing into wastewater | Stain-resistant fabrics, food packaging, cosmetics |
Industrial discharge from PFAS makers and users
The most direct route is discharge from facilities that manufacture PFAS or use them in production. EPA lists “manufacturing or chemical production facilities that produce or use PFAS,” including chrome plating shops and electronics makers, as key contamination sources. These sites can release PFAS into rivers through treated or untreated wastewater and into the air through emissions. Textile mills that make water-repellent fabric, paper mills, and metal finishers all fall into this category. Because the discharge is often continuous, industrial sources can build up very high PFAS levels in nearby surface water and groundwater over many years.
Firefighting foam at bases, airports, and training sites
Aqueous film-forming foam, usually shortened to AFFF, is a firefighting foam designed to smother fuel fires. For decades it was made with PFAS. Every time it was sprayed, whether on a real fire or during routine training drills, the foam soaked into the ground. From there, the Agency for Toxic Substances and Disease Registry (ATSDR) explains, PFAS “enter the ground, move into the groundwater to offsite locations,” and reach municipal wells located downhill from the source.
This pathway is a major reason PFAS contamination clusters around certain facilities. As of June 2024, the U.S. Department of Defense had identified 718 military installations with a known or potential PFAS release, most tied to AFFF use. Civilian airports and municipal fire training grounds add to the total. If you rely on a private well, the risk is worth understanding in detail, which our guide to PFAS in well water covers.
Landfill leachate
Landfills hold enormous quantities of PFAS-treated waste: old carpets, packaging, textiles, and industrial byproducts. When rain filters down through that buried waste, it picks up dissolved PFAS and forms a liquid called leachate. EPA identifies landfills and disposal sites among the settings where PFAS accumulate. Many landfills collect leachate and send it to a wastewater treatment plant, but as the next section explains, those plants were never built to remove PFAS, so the chemicals often pass straight through and back into waterways.
Wastewater treatment and land-applied biosolids
Conventional sewage treatment plants remove solids, bacteria, and many pollutants, but they do not break down PFAS. As a result, PFAS leave the plant in two ways. The first is treated water, or effluent, discharged into rivers and lakes. The second is biosolids, the solid material left over after treatment, which is often processed into fertilizer and spread on farmland. EPA notes that “fertilizer from wastewater treatment plants that is used on agricultural lands can affect ground and surface water.” Rain then washes PFAS off treated fields and into nearby streams and groundwater, spreading contamination into agricultural regions far from any factory.
Atmospheric deposition
Not all PFAS travel through water from the start. Some are released into the air from manufacturing facilities and incinerators, drift on the wind, and settle back onto land and water in rain, snow, and dust. This is called atmospheric deposition. It helps explain why low levels of PFAS appear in remote lakes and rainwater with no nearby industry. Once deposited, the same persistence and mobility take over, and the PFAS work their way into surface water and groundwater.
Consumer product breakdown
Everyday products treated with PFAS also contribute. Stain-resistant carpets and upholstery, waterproof clothing, grease-resistant food packaging, nonstick coatings, and some cosmetics shed small amounts of PFAS during normal use, washing, and disposal. Much of this ends up in household wastewater, which flows to treatment plants that cannot filter it out. Individually these releases are tiny, but across millions of households they add a steady background load to the water system. Learning to spot treated products is a practical first step, and our overview of what PFAS are explains where they hide.
What this means for your water
Because PFAS enter water from so many directions and resist breaking down, they are now found in water supplies nationwide rather than only near obvious pollution sites. That is the central takeaway of the USGS tap water study. The good news is that certain treatment methods do reduce PFAS at the tap, even though municipal plants generally do not. If you want to understand testing, regulation, and what the numbers mean for your household, start with our guide to PFAS in drinking water. If you are ready to act, our comparison of the best water filters for microplastics and PFAS walks through the options that actually work.
FAQ
How does PFAS get into drinking water?
PFAS reach drinking water through several routes: industrial discharge into rivers and groundwater, firefighting foam soaking into soil, landfill leachate, treated wastewater and biosolids from sewage plants, PFAS falling from the air, and consumer products breaking down. Once in the environment, PFAS move easily into the groundwater and surface water that many communities draw from.
What is the single biggest source of PFAS in water?
There is no single biggest source for every location. Industrial discharge and firefighting foam (AFFF) tend to create the most concentrated contamination near specific sites, while wastewater, biosolids, and atmospheric deposition spread lower levels of PFAS across wide areas. The dominant source depends on what facilities and land uses are near a given water supply.
How much of U.S. tap water contains PFAS?
The U.S. Geological Survey estimated in a 2023 study that at least 45% of the nation’s tap water contains one or more types of PFAS. The study tested for only 32 of the thousands of known PFAS, so researchers noted the real figure is likely higher.
Why are PFAS so hard to keep out of water?
PFAS are built around an extremely strong carbon-fluorine bond, so they do not break down naturally and can persist for a very long time. Many are also highly mobile, meaning they dissolve in water and do not cling to soil. That combination lets them travel long distances through groundwater and rivers, reaching wells and taps far from the original release.
Does boiling water remove PFAS?
No. Boiling does not remove PFAS and can actually concentrate them slightly as water evaporates. Removing PFAS requires specific treatment such as activated carbon filtration, reverse osmosis, or ion exchange. See our guide to water filters for the methods proven to reduce PFAS at the tap.
