The argument against putting Fluorine in our drinking water.

Fluorine and the other halogens are in the tan column, on the right side of the periodic table.  This means they are one electron short of a complete outer shell.  If they can grab that electron from another element they will become a noble gas, like Neon etc. (noble gases don't react with anything).  They are HUNGRY, and highly reactive.  The easiest place to find that electron is Carbon, which has 4 electrons which it is very happy to share.  So any organic molecule is a ripe target for attack by F, thus, not a good idea to be drinking it in water.  I keep my drinking water in a glass jug in the fridge so the Cl can evaporate, which it does very quickly.