Here's an interesting one.
I grew up without flouridated water and had really soft teeth. But it had nothing to do with the water. It was diet. Fixed the diet and the teeth hardened up so much the dentist comments changed to "see you if you break something".
Flouride works best applied directly to the surface of teeth. Brushing with flouridated toothpaste does this very well. Adding it to water does SFA.
If you want to make a difference to the worst kids teeth. You'll need to start flouridating coke.

