PFOA and PFOS are two synthetic chemicals that contaminate drinking water supplies across the United States. They belong to a larger family of compounds called PFAS, often nicknamed “forever chemicals” because they don’t break down naturally in the environment or in your body. The EPA now limits both PFOA and PFOS to 4.0 parts per trillion in drinking water, one of the strictest standards ever set for a drinking water contaminant.
What PFOA and PFOS Actually Are
PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) are man-made molecules built on a chain of carbon atoms bonded to fluorine. That carbon-fluorine bond is one of the strongest in chemistry, which is exactly why these compounds were so useful in manufacturing and exactly why they persist in the environment for decades or longer. Nothing in nature efficiently breaks them apart.
Their defining trait is the ability to repel both oil and water simultaneously. That made them ideal for an enormous range of products: nonstick cookware coatings, stain-resistant carpet and clothing treatments, waterproof outdoor gear, grease-resistant food packaging, and firefighting foam designed to smother fuel fires. PFOS was a key ingredient in firefighting foam (known as AFFF) used at military bases, airports, and training facilities through 2001. PFOA was widely used in manufacturing nonstick coatings like Teflon.
How They Get Into Drinking Water
PFOA and PFOS enter water supplies through several routes, all tied to industrial activity. Manufacturing facilities that produced these chemicals, or used them to make other products, released them into surrounding air, water, and soil for decades. From there, the compounds migrated into groundwater and surface water that feeds public water systems.
Firefighting foam is another major source. Every time AFFF was used in training exercises, sprayed during emergencies, or leaked from storage tanks and supply lines, PFOS-based chemicals soaked into the ground. Communities near military bases, airports, and industrial fire training sites are disproportionately affected. Landfills that accepted PFAS-containing consumer products also leach these chemicals into surrounding groundwater over time.
Because PFOA and PFOS don’t degrade, contamination from activities that ended years or even decades ago can still show up in water supplies today.
Health Effects of Exposure
These chemicals accumulate in the body over time, and they leave very slowly. The estimated half-life of PFOA in the human body ranges from about 2 to 10 years. For PFOS, it’s even longer: 3 to 27 years. That means if you stop all exposure today, it could take decades for your body to clear what’s already there.
Peer-reviewed research links prolonged exposure to a range of health problems:
- Cancer: Increased risk of kidney, testicular, and prostate cancers.
- Immune suppression: Reduced ability to fight infections and a weaker response to vaccines.
- Reproductive harm: Decreased fertility and higher rates of high blood pressure during pregnancy.
- Developmental delays in children: Low birth weight, earlier puberty, bone changes, and behavioral differences.
- Metabolic disruption: Elevated cholesterol levels and increased risk of obesity.
- Hormone interference: Disruption of the body’s natural hormone signaling.
The health risks aren’t limited to high-dose industrial exposures. Many of these effects have been observed at relatively low levels of chronic exposure, which is why the EPA set such a tight limit on drinking water concentrations.
The EPA’s Drinking Water Standards
In 2024, the EPA finalized legally enforceable limits for six PFAS chemicals in drinking water. PFOA and PFOS each received a maximum contaminant level (MCL) 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-sized swimming pools. The standard is extremely low because these chemicals are harmful at very small concentrations and build up in the body over years.
For four other PFAS chemicals (PFHxS, PFNA, PFBS, and GenX), the EPA uses a different approach called a Hazard Index. Rather than setting individual limits, the rule looks at the combined concentration of these chemicals in a mixture. Each chemical’s measured level is divided by its health-based threshold, and those fractions are added together. If the total exceeds 1, the water system is in violation. This accounts for the fact that multiple PFAS chemicals in smaller amounts can still pose a collective risk.
How to Find Out If Your Water Is Affected
Public water systems are required to test for PFAS using EPA-approved laboratory methods (Method 537.1 and Method 533), which use specialized techniques to detect these chemicals at parts-per-trillion levels. Your water utility’s annual Consumer Confidence Report should include PFAS results once testing is complete. Many utilities post these reports online.
If you’re on a private well, testing is your responsibility. You can send a sample to a certified lab that uses the same EPA methods. Expect to pay roughly $200 to $400 for a comprehensive PFAS panel, though prices vary by lab.
Removing PFOA and PFOS From Water
Standard water treatment processes like chlorination and basic filtration do very little against PFAS. These molecules are too chemically stable. However, two technologies work well.
Granular activated carbon (GAC) filters can be 100 percent effective at removing PFOA and PFOS, but performance depends on the type of carbon, the depth of the filter bed, water flow rate, temperature, and what else is in the water. Over time, the carbon becomes saturated and needs replacement. Many municipal water systems are installing large-scale GAC treatment, and point-of-use carbon filters rated for PFAS removal are available for home use.
Reverse osmosis (RO) systems are typically more than 90 percent effective at removing a wide range of PFAS, including shorter-chain varieties that carbon filters sometimes miss. Under-sink RO units are a practical option for filtering drinking and cooking water at home. They do produce wastewater, so they’re best used at the point of use rather than for your whole house.
If you’re shopping for a home filter, look for one that has been independently tested and certified specifically for PFOA and PFOS reduction. Not all carbon filters or pitcher-style filters are effective against these chemicals, and marketing claims don’t always match lab performance.
Why They’re Called “Forever Chemicals”
The nickname isn’t hyperbole. PFOA and PFOS resist heat, resist chemical reactions, resist biological breakdown, and resist photodegradation from sunlight. They don’t decompose in soil, don’t break down in water, and persist in the human body for years. Even though major U.S. manufacturers phased out production of PFOA and PFOS in the early 2000s, the compounds already released into the environment remain there. They cycle through soil, groundwater, rivers, and oceans essentially indefinitely. Replacement PFAS chemicals now in use have shorter carbon chains and leave the body faster, but many share similar concerns, which is why the EPA’s new rules cover multiple PFAS compounds beyond just the original two.