Question 1

What is Perfluorooctane Sulfonic Acid?

Accepted Answer

Perfluorooctane Sulfonic Acid (PFOS) is a per- and polyfluoroalkyl substance (PFAS) – a synthetic chemical used in manufacturing, firefighting foam, and consumer products. It persists indefinitely in water and the human body.

Question 2

Is PFOS in my drinking water?

Accepted Answer

EPA UCMR5 testing (2023-2025) monitors PFOS at 6,800+ US water systems. Enter your ZIP code at KnowYourExposure.com to see if PFOS has been detected in your specific utility.

Question 3

What is the EPA limit for PFOS?

Accepted Answer

The EPA drinking water limit for PFOS is 4 parts per trillion (ppt). Utilities have until 2029 to reduce levels below this threshold under the 2024 PFAS Rule.

Question 4

What are the health effects of PFOS?

Accepted Answer

PFOS exposure has been linked to: Bladder cancer, Kidney cancer, Non-Hodgkin lymphoma. Long-term exposure increases risks even at low doses.

Question 5

How do I remove PFOS from my water?

Accepted Answer

Certified reverse osmosis systems remove 90%+ of most PFAS including PFOS. Activated carbon and ion exchange filters also work. Boiling does NOT remove PFAS – it concentrates them.

Question 6

What is the CAS number for Perfluorooctane Sulfonic Acid?

Accepted Answer

The CAS Registry Number for Perfluorooctane Sulfonic Acid is 1763-23-1.

PFOS: Health Effects, EPA Limits & Sources (2026)