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 do not break down in the environment or in the human body.
Why they’re called “forever chemicals”
The carbon-fluorine (C-F) bond is one of the strongest in chemistry — approximately 544 kJ/mol. PFAS are built on chains of these bonds, making them extraordinarily resistant to heat, water, oil, and biological degradation. Unlike most organic pollutants that eventually break down, PFAS persist indefinitely in soil and groundwater.
In the human body, PFAS accumulate in blood, liver, and other organs over years of exposure. The half-life of PFOA in human serum is approximately 3.5 years — meaning even if you stop all exposure today, it takes years for your body to clear it. Some shorter-chain PFAS have faster clearance, but still persist for months.
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 the single largest source of PFAS groundwater contamination in the U.S. Over 700 military installations have confirmed releases.
Nonstick cookware
Polytetrafluoroethylene (PTFE/Teflon) coatings release PFAS when overheated. Manufacturing waste from cookware plants has contaminated waterways in multiple states, including the Haw River in North Carolina.
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
PFAS manufacturers (3M, DuPont, Chemours) and users in semiconductor, electroplating, and chemical industries have discharged PFAS into surface water for decades, contaminating downstream drinking water intakes.
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 across Maine, Michigan, 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. The EPA estimates utilities will spend $1.5–3.7 billion annually to comply with the new MCLs.
Key pathway: AFFF training fires at military bases → PFAS infiltrates soil → reaches groundwater → enters municipal wells serving nearby communities. This pattern has affected thousands of communities near military installations across the U.S.
Health effects
Decades of epidemiological research — including the C8 Health Study following 69,000 people near a DuPont plant — have established links between PFAS exposure and a range of serious health effects.
Cancer
Kidney cancer (RR ~1.7 for PFOA), testicular cancer, bladder cancer, non-Hodgkin lymphoma. PFOA is classified as a Group 1 carcinogen (definite human carcinogen) by the International Agency for Research on Cancer (IARC, 2023).
Thyroid & hormonal
PFAS disrupt thyroid hormone synthesis and metabolism, affecting T3/T4 levels. Associated with thyroid disease, altered menstrual cycles, and reduced fertility in both men and women.
Immune system
Reduces vaccine antibody response in children. Higher PFAS exposure is associated with greater susceptibility to infectious disease. Some research suggests PFAS impair the immune system at levels below current MCLs.
Reproductive & developmental
Reduced birth weight and fetal growth restriction. PFAS crosses the placenta and accumulates in breast milk. Pre-eclampsia risk elevated. Sperm quality and male fertility effects documented.
Liver & cholesterol
Elevated total and LDL cholesterol (documented in C8 Health Study, 3M worker studies). Non-alcoholic fatty liver disease. Disrupted liver enzyme function at environmentally relevant exposure levels.
Cardiovascular
Emerging evidence links PFAS exposure to hypertension and cardiovascular disease, potentially mediated through cholesterol dysregulation and inflammation pathways.
EPA’s response: the NPDWR Final Rule
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 under UCMR 5 (the Fifth Unregulated Contaminant Monitoring Rule), notify the public of results, and come into compliance by April 2029.
Compound
MCL
Compliance deadline
Notes
PFOA
4 ppt
April 2029
Most studied; IARC Group 1 carcinogen
PFOS
4 ppt
April 2029
Dominant compound in AFFF
PFHxS
Hazard Index ≤1
April 2029
Combined with PFNA, HFPO-DA, PFBS
PFNA
Hazard Index ≤1
April 2029
Combined hazard index approach
HFPO-DA (GenX)
Hazard Index ≤1
April 2029
DuPont PFOA replacement compound
PFBS
Hazard Index ≤1
April 2029
3M PFOS replacement compound
ppt = parts per trillion. To put 4 ppt in perspective: it is equivalent to 4 drops of water in 1 billion liters — or one second in 8,000 years. PFAS are toxic at extraordinarily low concentrations because they bioaccumulate and do not clear quickly from the body.
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 a public notice in a newspaper of general circulation
Report results to the state primacy agency
Implement a compliance solution (treatment, blending, source water change) by April 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 exceeding MCLs must install BAT-compliant treatment by April 2029.
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 (typically 15–25% of influent volume) that requires separate management. 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. Effective for larger PFAS molecules. Lower energy costs than RO but somewhat less complete removal for short-chain PFAS. 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 federal MCLs (4 ppt for PFOA and PFOS; hazard index ≤1 for PFHxS, PFNA, HFPO-DA, and PFBS combined) and 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. Small systems (under 10,000 population) may qualify for a two-year compliance extension to April 2031.
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.