Jersey Water told the BBC it was testing different methods of reducing PFAS, the results of which would come next year.
Helier Smith, the utility's chief executive officer, said a new treatment plant - if required - could cost up to £210m.
He said: "That could add 70% to 110% on to customer bills, making water in Jersey the most expensive in the world.
"Nobody wants that, especially Jersey Water.
"We want to find a solution that's proportionate and cost-effective, and keeps bills as low as we can, really."
Ian Cousins, the panel's environmental expert, said in other places measures to tackle PFAS had been implemented within three to five years.
He thought the cost quoted by Jersey Water was an "exaggeration" and that the panel's lower-cost calculations were based on retro-fitting existing water treatment plants rather than building a new one.
Ministers are due to respond to the report in more detail later this year.
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