Standard amounts of fluoride in streams and rivers found in nature: ~0.15 - 1.2 ppm
Even ocean water is around 1.2-1.4 ppm
The utility companies' fluoride levels are around 0.7 ppm, right in line with nature.
All of the fearmongering over fluoride being added to utility water is overblown and not based on empirical evidence.
Health problems only become present at ~4.0ppm+ and no water system utilizes that much fluoride, not even close to it.
There are far more things in tap water to worry about. While the water that comes from the tap is likely the cleanest mass produced water in human history, the piping systems aren't really that clean. I prefer filtered water not because of fluoride, but because of all the other stuff.