The thing about toxicity is that concentration is very important. Something that is “highly toxic” when you are exposed to a macro-dose, say 1 gram, can be completely harmless when it comes to a micro-dose, such as 10 ppm. So just saying something is “highly toxic” is essentially meaningless. You need to find out what dosages are toxic, and then compare that to the dosages that are used in drinking water.
True and here is what a Harvard study has found out.
Impact of fluoride on neurological development in children
http://www.hsph.harvard.edu/news/features/fluoride-childrens-health-grandjean-choi/
DiHydrogen Monoxide is extremely caustic and is in virtually all our drinking water supplies.