That's a headline I recently read. The reason shown was that those who drink only bottled and filtered water do not get the fluoride that is in tap water. Governments began adding fluoride in water in the 1940s and incidents of cavities dropped almost by half. Lately, some researchers have concluded that their might be too much fluoride in water and are discussing the appropriate amounts to be added.
Seems like another unintended consequence of the green movement.