Water fluoridation is an illogical concept: it is to help with tooth decay, yet we are swallowing it! Fluoridated toothpaste has already solved the issue of applying fluoride to the teeth without the need to ingest it.
There is no known nutritional requirement for flouride. If you are eating paleo, there is little point in fluoridating your teeth.
But the question still remains: is fluoridated water it harmful to health?
One thing to consider for health issues is: what does Europe do? Europe generally takes a precautionary approach to health- things are supposed to be proven save. They also aren't as biased as the U.S. on this issue. Our government has been championing fluoridation and CDC lists water fluoridation as one of the 10 greatest public health achievements of the last century. This means that just like the "saturated fat is evil" dogma, it fluoridation is now something that has to be defended(, regardless of the science)reality of the science. Water fluoridation is almost non-existent in Europe.
The most common form of fluoride placed in our water is generally a toxic industrial waste product (they have found a cheaper way to get rid of it now!), not the same as the forms found naturally in water.
We do know that fluoride is highly reactive, and one direct effect is that it can make bones more brittle. It also competes with iodine, creating thyroid issues. Ironically it actually damages the teeth of children (fluorosis). Everything we know about it tells us it is a toxin to our body. Our body is more than capable of handling small amounts of toxins, but we are probably all overloaded now.
The only question that I think remains is: how bad is it? Maybe not that much. Maybe some people are very sensitive. It Fluoride is something we should work to eliminate from the water supply (your are being taxed for this privilege), and something that for optimal health we should avoid. You may have higher priorities, especially considering the cost and hassle of filtering fluoride.