What Are PFAS? The “Forever Chemicals” in Your Water
Per- and polyfluoroalkyl substances (PFAS) are a family of more than 12,000 synthetic chemicals that have been manufactured and used in industry and consumer products since the 1940s. They are called “forever chemicals” because the carbon-fluorine bond, one of the strongest in organic chemistry, means they break down very slowly and can build up in people, animals, and the environment over time.
Why they’re called “forever chemicals”
The carbon-fluorine (C-F) bond is among the strongest single bonds in organic chemistry. PFAS are built on chains of these bonds, which makes them resistant to heat, water, oil, and biological degradation. Unlike most organic pollutants, they persist in soil and groundwater for a very long time.
EPA: “Some PFAS chemicals can accumulate in the body over time.” Source ↗
Common sources
PFAS were used in hundreds of industrial and consumer applications. These are the primary contamination pathways.
Firefighting foam (AFFF)
Aqueous film-forming foam used at military bases, airports, and industrial fire training sites is a well-documented source of PFAS in groundwater near where it was used.
Fluoropolymer coatings
Nonstick and other fluoropolymer coatings rely on PFAS chemistry. Facilities that made or applied these coatings have been sources of PFAS releases to nearby water and air.
Food packaging
Grease-resistant packaging — fast-food wrappers, microwave popcorn bags, pizza boxes — uses PFAS coatings that migrate into food. FDA phased out most PFAS food-contact uses for food packaging as of 2024.
Waterproof clothing & textiles
Durable water repellent (DWR) treatments on outdoor gear, carpets, and upholstery contain PFAS that leach during washing and accumulate in wastewater treatment sludge spread on agricultural land.
Industrial discharge
Facilities that made or used PFAS, including chemical, electroplating and semiconductor plants, have discharged PFAS to rivers and lakes that serve as downstream drinking water sources.
Biosolids on farmland
Wastewater treatment plants cannot remove PFAS — it concentrates in sewage sludge spread as fertilizer. This pathway has contaminated private wells and aquifers in Maine, Michigan, and other agricultural states.
How PFAS get into drinking water
PFAS released from industrial sites, military bases, or agricultural land leach through soil into groundwater, or run off into surface water (rivers, lakes, reservoirs). Conventional drinking water treatment — including coagulation, flocculation, sedimentation, filtration, and chlorination — does not remove PFAS.
Effective PFAS treatment requires activated carbon filtration (GAC or PAC), high-pressure membrane systems (nanofiltration or reverse osmosis), or ion exchange resins — all of which are significantly more expensive than standard treatment. EPA estimated the rule’s quantified costs at about $1.5 billion a year (2022 dollars).
Key pathway: AFFF training fires at military bases → PFAS infiltrates soil → reaches groundwater → enters municipal wells serving nearby communities. This pathway has been documented near military installations, airports, and fire-training areas.
Health effects
In EPA’s words: “Current peer-reviewed scientific studies have shown that exposure to certain levels of PFAS may lead to:”
Reproductive effects such as decreased fertility or increased high blood pressure in pregnant women.
Developmental effects or delays in children, including low birth weight, accelerated puberty, bone variations, or behavioral changes.
Increased risk of some cancers, including prostate, kidney, and testicular cancers.
Reduced ability of the body's immune system to fight infections, including reduced vaccine response.
Interference with the body's natural hormones.
Increased cholesterol levels and/or risk of obesity.
In April 2024, EPA finalized the National Primary Drinking Water Regulation (NPDWR) — the first-ever federal MCLs for PFAS in drinking water. The rule applies to all ~66,000 community water systems and non-transient non-community systems in the U.S. serving approximately 300 million Americans.
Systems must complete initial monitoring by April 26, 2027, report results, and meet the MCLs by April 26, 2029. On May 20, 2026 EPA proposed two changes: moving the PFOA/PFOS compliance date to April 26, 2031 for systems that request it (Docket EPA-HQ-OW-2025-1742), and rescinding the PFHxS, PFNA, HFPO-DA and Hazard Index limits (Docket EPA-HQ-OW-2025-0654). Comment periods closed July 20, 2026. As of October 18, 2026 neither is final, so the 2024 rule applies as written.
Compound
Limit
Compliance deadline
Notes
PFOA
4.0 ppt
April 26, 2029
EPA proposed April 26, 2031 for systems that request it (not final)
PFOS
4.0 ppt
April 26, 2029
EPA proposed April 26, 2031 for systems that request it (not final)
PFHxS
10 ppt; Hazard Index
April 26, 2029
EPA proposed rescinding (not final)
PFNA
10 ppt; Hazard Index
April 26, 2029
EPA proposed rescinding (not final)
HFPO-DA (GenX)
10 ppt; Hazard Index
April 26, 2029
EPA proposed rescinding (not final)
PFBS
Hazard Index only
April 26, 2029
No individual MCL; Hazard Index proposed for rescission (not final)
ppt = parts per trillion. To put 4 ppt in perspective: it is about 4 drops in 20 Olympic swimming pools (2.5 million liters per pool, 0.05 mL per drop), or one second in 8,000 years. EPA set the health-based goal for PFOA and PFOS at zero and the enforceable limit at 4.0 ppt, considering what is feasible to measure and treat.
What the MCL means for water utilities
Any public water system detecting PFAS above the MCL must:
Notify customers within 30 days of confirmation of an MCL violation
Issue public notice by the methods your state requires
Report results to the state primacy agency
Implement a compliance solution (treatment, blending, source water change) by April 26, 2029
Continue monitoring quarterly until achieving compliance; annually thereafter
UCMR 5 monitoring (2023–2025) gave EPA the first national dataset on PFAS occurrence: approximately 1.9 million sample results from over 10,000 water systems. This data now powers compliance tracking across the country — and is the source of the detection data shown in this tool.
Treatment technologies
EPA designated four Best Available Technologies (BAT) for PFAS removal under the 2024 NPDWR. Systems must meet the MCLs by April 26, 2029 and may use any approach that achieves compliance; the BAT list identifies technologies EPA found effective. See how each one performs in the treatment bench.
Granular Activated Carbon (GAC)
The most widely deployed PFAS treatment technology. GAC filters adsorb PFAS onto activated carbon media. Effective for long-chain PFAS (PFOA, PFOS). Higher contact time improves performance. Spent carbon must be replaced or reactivated — a significant ongoing operating cost. Best suited for large systems with high flow rates.
Anion Exchange (IX) Resins
Single-use or regenerable resin systems that attract negatively charged PFAS molecules. Single-use resins (PFAS-selective) achieve lower effluent concentrations than GAC with smaller system footprints. Regenerable resins reduce media replacement costs but generate a concentrated brine waste stream requiring disposal. Well-suited for small and medium systems.
Reverse Osmosis (RO)
High-pressure membranes that reject PFAS along with other contaminants. Highly effective — achieves near-complete PFAS removal across all chain lengths. Produces a concentrated reject stream that requires separate management: 15–20% of the feed in EPA's cost model, 8–15% at the full-scale plants EPA reviewed. Higher capital and energy costs than carbon-based systems. Best for systems with multiple contaminant concerns.
Nanofiltration (NF)
Similar to reverse osmosis but operates at lower pressure and allows some monovalent ions to pass. EPA's Treatability Database reports high maximum removals for the PFAS studied; performance depends on the membrane selected. Lower energy costs than RO. Less widely deployed for PFAS than the other three BATs — typically evaluated when water softening is also needed.
Compliance roadmap for water utilities
Most utilities are currently in the monitoring and planning phase. Initial sampling must be completed by April 2027 before treatment installation deadlines apply. State drinking water programs — not EPA directly — issue permits, review sampling results, and guide utilities through compliance under the Safe Drinking Water Act.
1
Confirm monitoring requirements
Coordinate with your state primacy agency to confirm which PFAS compounds you are required to monitor, sampling frequency, and whether you are covered under UCMR 5 or must conduct independent sampling under the 2024 NPDWR.
2
Perform initial PFAS sampling
Use a state-certified laboratory and collect samples using EPA Method 537.1 or Method 533. Both methods are approved under the 2024 NPDWR. Initial monitoring must be completed by April 26, 2027.
3
Evaluate results against MCLs
Compare laboratory results to the federal MCLs in force: 4.0 ppt each for PFOA and PFOS; 10 ppt each for PFHxS, PFNA, and HFPO-DA; and a Hazard Index of 1 for mixtures of PFHxS, PFNA, HFPO-DA, and PFBS (the last four are proposed for rescission, not final). Check any more stringent state limits that apply in your jurisdiction.
4
If limits are exceeded: plan treatment and secure funding
Conduct a technology evaluation and pilot test to select an appropriate BAT. Apply for DWSRF funding, WIIN Act grants, or USDA Rural Development loans before beginning design. Ask your state primacy agency whether an exemption is available, and track EPA's proposed April 26, 2031 PFOA/PFOS date for systems that request it.
5
Public notification and consumer reporting
Systems exceeding MCLs must notify customers within 30 days of confirmation, include results in the annual Consumer Confidence Report, and continue quarterly monitoring until achieving compliance. EPA provides consumer notice templates on its PFAS Implementation Toolbox.
Check your water system
Use our interactive map and system lookup to see PFAS detection levels, compliance status, and settlement eligibility for any public water system in the U.S.