PFAS & Water Quality Glossary (31 Terms)

Plain-English definitions for 31 PFAS, contaminant, and water-quality terms – including AFFF, EPA, MCL, ppt, UCMR5, and the regulatory acronyms that show up in EPA notices and Consumer Confidence Reports.

Quick Answer

This index links to 31 pages organized into 14 categories for easy browsing.

A (3)

  • Action Level The concentration of a contaminant that triggers required treatment or public notification. The lead action level is 15 ppb.
  • Activated Carbon A filtration medium made from carbon-rich materials. Granular activated carbon (GAC) filters can remove 60-95% of PFAS from drinking water.
  • AFFF Aqueous Film-Forming Foam:firefighting foam containing PFAS, a major source of groundwater contamination near military bases and airports.

B (2)

  • Bioaccumulation The buildup of chemicals in living organisms over time. PFAS bioaccumulate in blood and organs because the body cannot break them down.
  • Biomonitoring Testing blood or urine samples to measure chemical exposure. CDC studies show 98% of Americans have detectable PFAS in their blood.

C (2)

  • C8 Another name for PFOA (perfluorooctanoic acid), called C8 because it has 8 carbon atoms. Made infamous by the DuPont contamination in Parkersburg, WV.
  • Contaminant Any substance found in water that may pose a health risk. PFAS and lead are among the most concerning contaminants in US drinking water.

E (1)

  • EPA Environmental Protection Agency:the US federal agency that sets drinking water standards and monitors contamination levels nationwide.

F (1)

  • Forever Chemicals A nickname for PFAS because they do not break down in the environment. They persist in water, soil, and the human body for decades.

G (1)

  • GenX A replacement chemical for PFOA, used by Chemours. Despite being marketed as safer, GenX has been found to cause health effects similar to legacy PFAS.

H (2)

  • Half-life The time it takes for half of a substance to break down. PFAS have extremely long half-lives:PFOS stays in the human body for 4-5 years.
  • HFPO-DA Hexafluoropropylene Oxide Dimer Acid, the chemical name for GenX. One of the newer PFAS compounds regulated under EPA UCMR5.

L (2)

  • Lead A toxic heavy metal that enters drinking water through corroded pipes. There is no safe level of lead exposure, especially for children.
  • Lead Service Line A pipe made of lead that connects the water main to a home. Millions of US homes still have lead service lines built before 1986.

M (2)

  • MCL Maximum Contaminant Level:the highest level of a contaminant allowed in drinking water by the EPA. The MCL for PFOA is 4 ppt.
  • MCLG Maximum Contaminant Level Goal:the level of a contaminant below which there is no known health risk. The MCLG for PFOA and PFOS is zero.

N (1)

  • ND Non-Detect:a lab result indicating the contaminant was not found above the detection limit. Does not mean zero contamination.

P (8)

  • PFAS Per- and polyfluoroalkyl substances:a class of 15,000+ synthetic chemicals used since the 1940s. Found in water, food packaging, nonstick cookware, and firefighting foam.
  • PFHxS Perfluorohexane sulfonic acid:a 6-carbon PFAS compound commonly found in firefighting foam contamination. Regulated under EPA UCMR5.
  • PFNA Perfluorononanoic acid:a 9-carbon PFAS compound. One of the six PFAS compounds with enforceable EPA limits as of 2024.
  • PFOA Perfluorooctanoic acid:one of the most studied PFAS compounds. Used in Teflon manufacturing. EPA limit: 4 parts per trillion.
  • PFOS Perfluorooctane sulfonic acid:the most commonly detected PFAS in US water. Previously used in Scotchgard and firefighting foam. EPA limit: 4 ppt.
  • PPB Parts Per Billion:a measurement unit for contaminant concentration. 1 ppb = 1,000 ppt. Lead is measured in ppb; the EPA action level is 15 ppb.
  • PPT Parts Per Trillion:the measurement unit for PFAS in water. EPA limits for PFOA and PFOS are 4 ppt. One part per trillion is like one drop in 20 Olympic swimming pools.
  • PWS Public Water System:any system that provides water for human consumption to at least 25 people or 15 service connections. Over 150,000 PWSs exist in the US.

R (2)

  • Reverse Osmosis A water filtration method that forces water through a semi-permeable membrane, removing 90-99% of PFAS and lead. One of the most effective home treatment options.
  • RO Reverse Osmosis:see Reverse Osmosis. RO systems are recommended by the EPA for PFAS removal at the household level.

U (3)

  • UCMR Unregulated Contaminant Monitoring Rule:EPA program requiring public water systems to test for specific unregulated contaminants. UCMR5 (2023-2025) tests for 29 PFAS.
  • UCMR3 The third cycle of EPA unregulated contaminant monitoring (2013-2015). Tested for 6 PFAS compounds across large water systems. Provides historical baseline data.
  • UCMR5 The fifth and most recent cycle of EPA monitoring (2023-2025). Tests for 29 PFAS compounds across all water systems serving 3,300+ people.

W (1)

  • Water System The infrastructure that collects, treats, and distributes drinking water. Each system has a unique PWSID (Public Water System ID) tracked by the EPA.