It's been researched for 75 years. Fluoride is only harmful at considerably higher doses than are put in the water.

If you are in the small group of people prone to dental fluorosis and need to remove fluoride from your water, a reverse osmosis filter will do the job.

But there is absolutely no indication that fluoride in water, at the levels we use it, causes any adverse health reaction except that some young children may get slight staining on their teeth...the teeth they are only keeping a few years anyway ;).