PFOA and PFOS are two synthetic chemicals that can contaminate drinking water and persist in the human body for years. They belong to a larger family of compounds called PFAS, sometimes nicknamed “forever chemicals” because they resist breaking down in the environment. In 2024, the EPA set the first legally enforceable limits for both chemicals in public drinking water at 4.0 parts per trillion, a level so low it reflects how seriously regulators view even tiny exposures.
What PFOA and PFOS Actually Are
PFOA stands for perfluorooctanoic acid. PFOS stands for perfluorooctane sulfonate. Both are man-made chemicals built on a chain of carbon atoms where every hydrogen atom has been replaced by fluorine. That carbon-fluorine bond is one of the strongest in chemistry, which is why these compounds don’t break down naturally in soil, water, or your body.
The two chemicals differ slightly in structure and size. PFOS has a higher molecular weight (500 g/mol compared to 414 for PFOA) and a sulfonate group at the end of its chain, while PFOA ends in a carboxylic acid group. This structural difference matters because it changes how each chemical behaves once it enters your body. PFOS sticks around much longer: its average half-life in humans is about 7.5 years, meaning it takes that long for your body to eliminate just half of the amount absorbed. PFOA clears faster, with an average half-life of roughly 2.4 years, though women tend to eliminate it more quickly (about 2 years) than men (closer to 2.8 years). Children under 14 clear PFOA fastest, at around 1.6 years.
How They Get Into Drinking Water
These chemicals were widely used in manufacturing from the 1950s onward. PFOA was a key ingredient in making nonstick coatings for cookware and water-resistant textiles. PFOS was the active ingredient in certain stain repellents and, critically, in aqueous film-forming foam (AFFF), a firefighting foam used at military bases, airports, and industrial sites for decades.
Firefighting foam is one of the single largest sources of groundwater contamination. When AFFF is sprayed during training exercises or fire suppression, it soaks into the ground and migrates into the water table. Communities near military bases, airports, and chemical manufacturing plants tend to have the highest contamination levels. But PFOA and PFOS also enter water systems through industrial discharge, wastewater treatment plants, and landfill runoff. Once in groundwater, they don’t degrade. They simply spread.
From contaminated water, these chemicals can also accumulate in food. Crops irrigated with contaminated water, livestock that drink it, and fish from affected waterways all carry PFAS into the food chain.
Why They’re Harmful
The health concerns around PFOA and PFOS aren’t theoretical. Decades of epidemiological research have linked exposure to a range of serious conditions: altered thyroid function, liver disease, disrupted cholesterol and insulin regulation, kidney disease, reproductive problems, and cancer. The evidence is particularly strong for immune suppression. In children, exposure is associated with higher rates of skin conditions like eczema and more frequent lower respiratory tract infections, suggesting these chemicals weaken the body’s ability to fight off illness.
Cancer risk has been studied extensively in heavily exposed populations, especially workers in chemical plants. Liver cancer mortality is elevated in those with high occupational exposure. Evidence is also accumulating for kidney cancer links, and longitudinal studies have detected increased testicular cancer risk from cumulative PFOA exposure.
One way these chemicals cause harm is by interfering with thyroid hormones. Your thyroid gland produces hormones (T4 and T3) that regulate metabolism, energy, and development. PFAS appear to disrupt the conversion of T4 into T3, the more active form, and may also block the uptake of iodine that the thyroid needs to function. This can alter hormone levels even when the gland itself appears normal on standard tests.
Current Drinking Water Limits
For years, the EPA offered only a non-enforceable health advisory for PFOA and PFOS. That changed in April 2024, when the agency finalized the first National Primary Drinking Water Regulation for PFAS. The legally binding maximum contaminant levels are set at 4.0 parts per trillion (ppt) for PFOA and 4.0 ppt for PFOS, each measured individually. 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 strict because these chemicals accumulate over time and cause harm at very low concentrations.
Public water systems are required to monitor for these contaminants and take action if levels exceed the limits. Most large utilities will need to install advanced treatment technologies, typically granular activated carbon filters or specialized membrane systems, to bring levels into compliance.
Testing Your Own Water
If you’re on a public water system, your utility will be responsible for testing and reporting PFAS levels as the new regulation takes effect. You can request their most recent water quality report or check for it online.
Private wells are a different situation. They aren’t covered by federal drinking water regulations, so testing falls on the homeowner. The EPA recommends contacting your state environmental or health agency for a list of state-certified laboratories that use EPA-approved testing methods for PFAS in drinking water. Standard home water tests don’t check for these chemicals, so you need to specifically request PFAS analysis. Costs typically range from $200 to $500 depending on the lab and the number of compounds tested.
If your water tests positive for elevated levels, in-home treatment options include activated carbon filters, reverse osmosis systems, and certain filtered pitchers that are certified to reduce PFAS. Look for certification from NSF International or the Water Quality Association specifically for PFAS reduction, not just general filtration. Regular retesting is also important, since contamination levels can change over time as groundwater conditions shift.
Why These Chemicals Persist
The “forever chemical” label isn’t hyperbole. The carbon-fluorine bonds in PFOA and PFOS resist heat, water, oil, and biological degradation. Standard water treatment processes like chlorination and basic filtration don’t remove them. In soil, they don’t break down over any meaningful human timescale. And in your body, they bind to proteins in the blood and accumulate in organs, particularly the liver and kidneys, cycling through your system for years before being slowly excreted.
This persistence is exactly what made them so useful in industrial applications. Nonstick coatings, waterproof fabrics, and firefighting foams all relied on the same chemical stability that now makes these compounds so difficult to clean up. Major manufacturers voluntarily phased out production of PFOA and PFOS in the early 2000s, but the chemicals already released into the environment remain. They’re now detectable in the blood of virtually every person tested in industrialized countries, at varying concentrations depending on proximity to contamination sources and dietary exposure.