MCL (Maximum Contaminant Level)
The highest level of a contaminant allowed in drinking water, set by the EPA.
Maximum Contaminant Levels are legally enforceable standards that public water systems must meet. In 2024, the EPA finalized MCLs for six PFAS compounds: PFOA and PFOS at 4 ppt each, PFHxS/PFNA/HFPO-DA at 10 ppt each, and a hazard index for mixtures. Water systems have 3-5 years to comply.