PFAS in well water: PFOA, PFOS limits and filters
The EPA limit is 4 ng/L (parts per trillion) each for PFOA and PFOS. Health Canada's objective is 30 ng/L for the total of 25 PFAS. Above these, use another source for drinking and ask about a certified filter.
- US (EPA)
- 4 ng/L for PFOA and 4 ng/L for PFOS. EPA has proposed dropping its limits for other PFAS.
- Canada
- 30 ng/L for the sum of 25 PFAS (Health Canada objective).
What it is
PFAS are man-made "forever chemicals" used in firefighting foam, nonstick and stain resistant products. They reach wells near airports, military bases, landfills, factories and fields where biosolids were spread. They are measured in nanograms per liter (ng/L), the same as parts per trillion (ppt).
What your number means
- Within limitsBelow 2 ng/L
Under half the EPA limit for PFOA or PFOS.
- Close to limit2 to 4 ng/L
Under the limit. Retest within a year.
- Above limitAbove 4 ng/L
Use bottled water for drinking and cooking, contact your health department, and ask about a certified filter.
What to do
- Above the limit, use bottled water for drinking, cooking and infant formula for now.
- Contact your health department. Many states have PFAS programs that test nearby wells or help pay for treatment.
- Ask about point of use reverse osmosis or a carbon filter certified to reduce PFOA and PFOS (NSF/ANSI 53 or 58), and replace filters on schedule.
- Boiling does not remove PFAS.
How often to test
If you are near a known source, test once and follow your health department's advice. Retest every year if you have treatment, to check the filter still works.
Common questions
Do PFAS limits apply to private wells?
The EPA limits are for public water systems, but health departments use them to advise well owners too.
What is the difference between ng/L and ppt?
None. One nanogram per liter is one part per trillion.
Sources: EPA PFAS drinking water rule; Health Canada: PFAS in drinking water. Limits checked November 2026.