Plain English

Acronyms & terms, decoded

Every acronym and technical term you'll encounter on CheckPFAS, defined in plain English with the regulatory or scientific context that matters. Hover any underlined acronym on the rest of the site to see the short definition; click through for the long version.

AFFF

Aqueous Film-Forming Foam

Firefighting foam responsible for major PFAS groundwater contamination.

A fire-suppression foam used at military bases, airports, and industrial facilities since the 1960s. Historical AFFF formulations contained high concentrations of PFOS and PFOA, making AFFF responsible for some of the worst PFAS groundwater contamination in the US. The Department of Defense has identified over 700 contaminated AFFF sites.

ATSDR

Agency for Toxic Substances and Disease Registry

US federal agency that publishes the PFAS Toxicological Profile.

A federal public-health agency within the US Department of Health and Human Services. Publishes Toxicological Profiles for hazardous substances, including the canonical PFAS Toxicological Profile that this site treats as a primary source for health-effect claims.

C8

Common name for PFOA

Industry shorthand for the 8-carbon PFOA molecule.

Industry shorthand for PFOA, named for its 8-carbon backbone. Also the name of the "C8 Health Project" — a large epidemiological study of 70,000 people exposed to PFOA via contaminated drinking water near a DuPont manufacturing plant in Parkersburg, West Virginia. The C8 Study's findings underlie much of what we know about PFOA health effects.

CCR

Consumer Confidence Report

Your water utility's annual report on water quality.

A report that every public water utility in the US is required to publish annually, by July 1, covering the previous calendar year's water quality. It includes contaminant test results, detected levels, the utility's compliance status, source-water information, and risk language. The CCR is the most authoritative source on water actually reaching your tap.

EPA

United States Environmental Protection Agency

The US federal agency that sets and enforces drinking-water standards.

The US federal agency responsible for environmental regulation, including the Safe Drinking Water Act, the Unregulated Contaminant Monitoring Rule (UCMR), and the National Primary Drinking Water Regulations under which PFAS MCLs were finalized in April 2024. Every PFAS data point on CheckPFAS originates from the EPA's UCMR 5 occurrence dataset.

GAC

Granular Activated Carbon

Carbon-based filtration that adsorbs long-chain PFAS.

A filtration method using porous activated-carbon granules (often coconut-shell-derived). PFAS molecules chemically bond to the carbon surface and are trapped. Effective for long-chain PFAS (PFOA, PFOS) but less reliable for short-chain compounds. Available in pitcher form ($30–$100) and under-sink units ($100–$300).

GenX

Common name for HFPO-DA

Trade name for the PFOA replacement chemistry sold by Chemours.

The trade name for HFPO-DA chemistry, introduced by Chemours in 2009 as a PFOA replacement at the Fayetteville Works plant in North Carolina. GenX has become emblematic of the "regrettable substitution" problem — replacing one PFAS with another whose health effects only became clear after widespread environmental release.

GW

Groundwater

Water sourced from underground aquifers via wells.

Water sourced from underground aquifers accessed via wells. One of the two source-water categories for public water systems. Groundwater systems near industrial facilities, military bases, or agricultural land often show higher PFAS concentrations due to soil infiltration.

IARC

International Agency for Research on Cancer

WHO body that classifies carcinogenic risk.

An agency of the World Health Organization that evaluates the carcinogenic risk of chemicals to humans. Classifications: Group 1 (carcinogenic), Group 2A (probably carcinogenic), Group 2B (possibly carcinogenic), Group 3 (not classifiable). In November 2023, IARC reclassified PFOA as Group 1 and PFOS as Group 2B.

MCL

Maximum Contaminant Level

The EPA's legal limit for a contaminant in drinking water.

A federally enforceable ceiling on the concentration of a contaminant in public drinking water. Water utilities must monitor for the contaminant and take corrective action — including notifying customers — if levels exceed the MCL. EPA finalized the first US PFAS MCLs in April 2024: 4 ppt for PFOA and PFOS, 10 ppt for PFNA, PFHxS, and HFPO-DA.

MRL

Minimum Reporting Limit

The lowest concentration a lab method can reliably quantify.

The lowest PFAS concentration that the EPA's analytical method can detect with confidence — roughly 1.5–2 ppt for most PFAS compounds under UCMR 5. A "Not detected" result on a CheckPFAS page means the sample came back below the MRL, not literally zero. Lab instruments have detection floors.

NSF

NSF International

Independent organization that tests and certifies water treatment products.

An independent product-testing organization headquartered in Michigan. NSF certifies water-filter products against ANSI-developed standards. Three standards matter for PFAS removal: NSF/ANSI 58 (reverse osmosis), NSF/ANSI 53 (general health-effect contaminant reduction), and NSF P473 (PFAS-specific certification for PFOA and PFOS).

NSF P473

PFAS-Specific NSF protocol

NSF protocol that directly verifies PFOA and PFOS reduction.

A NSF protocol that specifically validates a filter's ability to reduce PFOA and PFOS — the two PFAS compounds with the strictest EPA limits. The most relevant certification for PFAS-contaminated water. Filters carrying both NSF/ANSI 53 and NSF P473 are the most rigorously vetted for PFAS removal at the consumer level.

NSF/ANSI 53

Health Effects certification standard

NSF standard for filters reducing health-effect contaminants.

The NSF/ANSI standard for filters that reduce contaminants with established health effects. Certifies carbon block and pitcher filters for lead, VOCs, and PFAS (when combined with P473 PFAS-specific testing). Must be combined with P473 for full PFAS assurance.

NSF/ANSI 58

Reverse Osmosis certification standard

NSF certification covering RO system contaminant reduction including PFAS.

The NSF/ANSI standard for residential reverse osmosis drinking water systems. Certifies RO units for reduction of contaminants including PFAS, lead, arsenic, and nitrates. The gold-standard certification for under-sink and countertop RO units.

PFAS

Per- and Polyfluoroalkyl Substances

"Forever chemicals" — a family of 12,000+ synthetic compounds.

PFAS are a family of more than 12,000 synthetic chemicals defined by an extremely strong carbon–fluorine bond — the strongest in organic chemistry. That bond is what makes them "forever chemicals": they don't break down naturally in the environment or in the human body. Five PFAS (PFOA, PFOS, PFNA, PFHxS, HFPO-DA) have enforceable US drinking-water limits; 24 more are under active monitoring.

ppt

Parts Per Trillion

Unit of measurement equivalent to 1 nanogram per liter.

The unit used to express PFAS concentrations in drinking water. 1 ppt = 1 nanogram per liter (ng/L). To visualize: 4 ppt is equivalent to 4 drops of water in 250 Olympic-sized swimming pools. These levels sound vanishingly small, but PFAS accumulate in the body over years.

PWSID

Public Water System Identifier

EPA's unique ID for each public water system.

A state-prefixed alphanumeric code assigned by the EPA to every public water system in the US. Used to track testing results across federal datasets including UCMR 5 and SDWIS. A PWS (Public Water System) is any entity providing drinking water to 25+ people or 15+ connections year-round.

RO

Reverse Osmosis

Filtration that physically blocks PFAS at the molecular level.

A filtration process that forces water through a semi-permeable membrane under pressure, physically blocking PFAS molecules. The most effective consumer technology for PFAS removal: 90–99.9% reduction across all chain lengths. Available as under-sink systems ($150–$600) or countertop units. Wastes some water and removes most minerals — a trade-off some readers care about.

SW

Surface Water

Water sourced from rivers, lakes, and reservoirs.

Water sourced from rivers, lakes, and reservoirs. The other public-water-system source-water category. Surface water systems often face PFAS contamination from upstream industrial discharges, AFFF runoff, or treatment-plant biosolids application.

UCMR

Unregulated Contaminant Monitoring Rule

The EPA program that periodically monitors emerging contaminants.

A federally mandated testing program under the Safe Drinking Water Act. Every five years, the EPA selects a list of unregulated contaminants and requires public water systems to test for them. The data informs future regulatory decisions. Now in its fifth cycle (UCMR 5, 2023–2025), which focused on PFAS.

UCMR 5

EPA's Fifth Unregulated Contaminant Monitoring Rule

The 2023–2025 EPA program that tested ~10,000 water systems for PFAS.

The fifth cycle of the EPA's UCMR program, covering 2023–2025 with results released in January 2026. Required all US public water systems serving more than 25 people to test for 29 PFAS compounds plus lithium. Every result on CheckPFAS comes from UCMR 5. This was the most comprehensive federal PFAS testing program ever conducted in the United States.