It probably can't be effectively filtered at utility scale. There are only a small number of effective filtration methods and they basically coalesce to either distillation or reverse osmosis, neither of which is effective at utility scale. The other side of that is that both methods concentrate contaminates when removing them, and distillation puts some contaminates into the air, which means neither is a panacea even at residential scale.

The largest reverse osmosis plant in the world produces 165MGD of water, which is less than is required for any of the top 10 largest US cities, while primarily being used purely for desalination (SWRO). At the levels of filtration and membrane size required for removal of PFAS, it would nearly be impossible to cost effectively filter 200MGD+ of water for a major city.