water. The PURE EFFECTS ULTRA
removes fluoride and radioisotopes
like those from Fukushima.
Both Inline and Countertop versions are available. I'm using the countertop version and can attest to it's fluoride removal efficacy.
UPDATE: The cheaper one or two-filter units will now remove radio-isotopes with the Zeolite filter, but may not reduce fluoride. This is still better than nothing and therefore worth checking out.