I believe back in the 90's activists in some U.S. cities got their cities to stop adding fluoride to the supplies. Bad mineral exchanges immediately started to occur in the piping because of the accumulated minerals in the pipes which included a fluoride component started reacting with the water that no longer contained fluoride causing the water to become contaminated by minerals other than just fluoride. The water not only tasted bad, it was determined that it was not safe to drink.
It takes decades for the minerals in the piping to accumulate and it will take decades to slowly taper fluoride away if we want to avoid unintended consequences. I know the mineral content of water varies widely across supply sources so some cities may have no related problems and some could have severe problems.