While I can't source the IQ claim, the evidence "showing" that fluoridation is safe to drink (as opposed to measuring by tooth health) is fairly scarce.

OTOH I've heard teeth are especially poor around Portland Oregon where they don't fluoride the water. I'd simply say the jury is still out.

I tend to think of iq claims specifically with a particularly large grain of salt: it's an index of society that people follow closely and is related to many, many factors.