Fluoride in drinking water has no effect on IQ or brain function, long-term study shows
(twin-cities.umn.edu)
the first major study in fluoride, the Grand Rapids study would never hold up to today’s standards. It was not a blind study and cavity detection is subjective.
There has been many more studies on fluoride, none of which have shown that that the low concentrations of fluoride added to drinking water has any negative health effect. Not just the one, always check multiple sources!
Also drinking water is a poor way to deliver fluoride
It depends on the area you're dealing with. In some countries, it's more cost effective to put fluoride in the water supply, while in others, fluoride toothpastes are more effective. In Germany, they put fluoride in iodized salt!