Fluoridated Countries Compared to Non-Fluoridated Ones. 
 

Take a look at these two graphs.

The first one shows the falling rates of tooth decay in the US after the introduction of fluoride.

This is the document that is still used today to show the effectiveness of fluoride and it looks pretty convincing.

That is, until you look at the second one.

Eighteen countries are shown in this one and in all of them tooth decay rates had fallen dramatically.
Only four of these countries are fluoridated.
It's clearly not fluoridated water that is producing this improvement and if it doesn't work, why add it?

Note that the source of this second graph is the WHO.