Receiving PFAS water test results from a certified laboratory can be confusing without context. Understanding the units, regulatory benchmarks, and what action different results call for helps translate numbers into practical decisions about filtration and health protection.
Units of Measurement
PFAS concentrations in water are measured in nanograms per liter (ng/L), which are equivalent to parts per trillion (ppt). One part per trillion is an extraordinarily small concentration — equivalent to one drop of water in an Olympic swimming pool. Despite this seemingly tiny scale, PFAS health effects occur at these very low concentrations due to their persistence and bioaccumulative properties.
Comparing Results to Current Standards
The EPA’s 2024 final rule established maximum contaminant levels (MCLs) of 4 ppt for PFOA and PFOS individually. For PFNA, PFHxS, and HFPO-DA (GenX), the MCL is also 4 ppt each. For combinations of certain PFAS, a hazard index limit of 1.0 applies. Compare your results against these benchmarks to assess whether regulatory levels are exceeded.
Results Below Detection Limits
Laboratories report results below their method detection limit as “not detected” or “< [detection limit]." A not-detected result does not guarantee complete absence of PFAS — it means concentrations are below the laboratory's analytical sensitivity. For PFOA and PFOS, modern EPA methods detect at 0.5 ppt or lower, providing meaningful assurance when results come back as not detected.
Deciding on Filtration
Results above EPA MCLs indicate filtration or another source of drinking water is warranted. Results below MCLs but above health advisories may still call for filtration depending on household risk factors. Even not-detected results may justify precautionary filtration in households with pregnant women, infants, or individuals with prior PFAS-related health conditions.