2x is honestly pretty small. I would expect the amount required to drop IQ to be larger by an order of magnitude or more to conclude that fluoridating water is totally safe.

So if your training and double your water intake your basically lowering you IQ? (according to the Chinese studies) I wonder the method this uses.. has anyone looked at dementia rates in high fluoride areas.. Particularly in people with high water intake?

There is also a host of things we use water for from cooking to preserving, distilling and cooling.. i wonder if any of these things could concentrate the fluoride.

Also since fluoride has a lower boiling point any studies tracked what breathing in fluoride gas over long periods cause?

2x is basically no safe margin for something like water. Of course you can question the quality of the study, but if it's actually 2x, fluoride in tap water should be treated like lead pipes.