I think it's been known even longer than that, though possibly for higher levels of fluoride. Prevention magazine (which my mother sends me) recently had an article on the dangers of water fluoridation. Thought it was pretty gutsy of them, given their usual reporting. Part of it discussed brown-stained teeth caused by naturally occurring high fluoride levels in a few towns before water fluoridation became widespread--I think maybe around the turn of the century, even...

In fact, here's their timeline and article.

We're on non-fluoridated well water here, and I'm rather glad there's no added chlorine and fluoride in it, even if we do need to do something about the coliform bacteria that finds its way in.