PFAS are a group of synthetic chemicals found in roughly 45% of U.S. tap water, according to a nationwide sampling study. Short for per- and polyfluoroalkyl substances, they’re often called “forever chemicals” because they don’t break down naturally in the environment or in your body. They enter drinking water from industrial sites, military bases, and everyday consumer products, and even at very low concentrations they’ve been linked to serious health problems.
Why PFAS Don’t Break Down
PFAS molecules are built around chains of carbon atoms bonded to fluorine. The carbon-fluorine bond is one of the strongest in organic chemistry, and that’s what makes these chemicals so useful in nonstick coatings, waterproof fabrics, and food packaging. It’s also what makes them so dangerous. Natural processes like sunlight, bacteria, and water simply can’t break these bonds apart under normal conditions. Once PFAS enter soil or water, they persist for decades or longer, cycling through the environment and accumulating in living organisms along the way.
There are thousands of individual PFAS compounds. The most studied are PFOA and PFOS, both “long-chain” varieties with eight carbon atoms. Manufacturers began phasing these out in the early 2000s, but replaced them with “short-chain” alternatives like GenX (six carbon atoms). These newer compounds don’t accumulate as readily in the human body, but they’re just as persistent in the environment and actually more mobile in groundwater, meaning they can travel farther from their original source.
How PFAS Get Into Drinking Water
The biggest known sources are firefighting foams, industrial manufacturing, and wastewater treatment plants. Fluorine-containing foams have been used since the 1960s to extinguish fuel-based fires involving gasoline and kerosene. Decades of training exercises at military bases, civilian airports, and oil refineries saturated the surrounding soil, allowing PFAS to seep into groundwater over time.
Manufacturing plants that produce or use PFAS discharge them into nearby waterways. Wastewater treatment facilities are another pathway: they receive PFAS from household products and industrial waste but aren’t designed to remove them, so the chemicals pass through into rivers and lakes that feed downstream water supplies. Agricultural land treated with biosolids (essentially processed sewage sludge used as fertilizer) is a growing concern as well, since PFAS in the sludge leach into groundwater and irrigation sources.
Health Risks of PFAS Exposure
The EPA’s current assessment ties PFAS exposure to a broad range of health effects. These include increased risk of prostate, kidney, and testicular cancers, elevated cholesterol, reduced immune function (including weaker responses to vaccines), and interference with the body’s hormones. Pregnant women face specific risks: decreased fertility and higher rates of high blood pressure during pregnancy. Children exposed to PFAS may experience low birth weight, earlier puberty, and behavioral changes.
What makes PFAS particularly concerning is how long they linger in the body. Once you ingest them through drinking water, they bind to proteins in your blood and tissues. PFOA takes roughly 2 to 10 years to drop to half its concentration in your body. PFOS can take 3 to 27 years. One compound, PFHxS, has a half-life of up to 35 years. Shorter-chain replacements like PFBS clear much faster (weeks rather than years), but their long-term effects are still being understood. The slow elimination means that even modest daily exposure through tap water builds up over time.
Current Legal Limits
In 2024, the EPA set the first legally enforceable limits for PFAS in drinking water. The two most common legacy chemicals, PFOA and PFOS, each have a maximum contaminant level of 4.0 parts per trillion. To put that in perspective, one part per trillion is roughly equivalent to a single drop of water in 20 Olympic swimming pools. Three other individual compounds (PFHxS, PFNA, and GenX chemicals) are capped at 10 parts per trillion each. When two or more of those compounds appear together, the EPA uses a combined “hazard index” to account for their additive effects.
Public water systems are required to test for these six PFAS and report results. Compliance is based on annual averages at each sampling point. Private wells, however, are not covered by this rule. If you rely on well water, testing is your responsibility.
How to Test Your Water
If your water comes from a public utility, your annual Consumer Confidence Report (available from your water provider or the EPA’s website) should begin including PFAS data as utilities comply with the new regulation. For private wells or if you want independent verification, you can send a sample to a certified laboratory. Labs use EPA-approved methods that can detect PFAS at concentrations as low as single-digit parts per trillion. A basic PFAS panel typically costs between $200 and $400, depending on how many compounds are tested.
Removing PFAS at Home
Not all water filters handle PFAS equally. Research from Duke University tested a range of in-home systems and found that reverse osmosis filters reduced PFAS levels by 94% or more, including newer compounds like GenX. Two-stage filters (which combine multiple filtration technologies) performed similarly well. Activated carbon filters, the type found in most pitcher-style and faucet-mounted units, removed an average of 73% of PFAS, but performance varied widely from brand to brand and dropped as filters aged.
If you’re choosing a filter specifically for PFAS, reverse osmosis systems installed under the sink or at the point of entry to your home offer the most reliable protection. Standard carbon pitcher filters are better than nothing but shouldn’t be your only line of defense if your water has confirmed contamination. Regardless of the type, replacing filter cartridges on schedule matters. PFAS removal rates decline as the filter media becomes saturated.
Who Faces the Highest Risk
People living near military bases, airports, or industrial facilities that used firefighting foam face the greatest likelihood of elevated PFAS in their water. Communities downstream from manufacturing plants or near farmland treated with biosolids are also at higher risk. Private well users in these areas are especially vulnerable because they lack the monitoring and treatment infrastructure of public water systems.
Geography isn’t the only factor. Because PFAS accumulate over a lifetime, older adults carry higher body burdens than younger people with the same exposure level. And because these chemicals cross the placenta and appear in breast milk, fetuses and infants are exposed during the most sensitive windows of development. The EPA’s 4-parts-per-trillion limits for PFOA and PFOS were set with these vulnerable populations in mind.