The answer depends on how much you have to spend, the flow rate, the fluoride concentration, and the water analysis. You have not provided any of this information.
The best technologies are reverse osmosis and distillation. These processes will remove 90%+ of the fluoride but will be expensive. If you do not want the expense of a distillation or a reverse osmosis system, you can try a filter with a cartridge containing activated alumina.
Activated alumina cartridges are relatively expensive and have a short like, but they do work.