Typical carbon filter may not catch fluoride. You have to distill usually and it might be cheaper to buy distilled water. The amount of fluoride varies but it's never healthy to swallow fluoride. Fortunately there is such a small amount usually in water that you'd spend your whole life swallowing it without it killing you but it depends on how long you live and on your particular reaction.

This might explain why so many people drink bottled water. Distilled water and bottled water is nice to have to drink.