Hey, thanks, guys! I think that I'm getting it. When MMario said that about their being roughly equal the rest fell into place.

Above optimum doses many medications are toxic. Rat poison is the active ingredient in some prescriptions, for instance. For that matter, common table salt is poisonous. Oh, and there is such a thing as WATER poisoning. Ya cain't win.

As for the question at hand, I know the man who wrote that letter to the editor and I wanted an idea of the validity of his argument. I'm not convinced of the utility or feasibility or necessity of fluoride-enhanced water; on the other hand, children today have much better teeth than do previous generations...