All this talk, and from others that F is a rat poison etc are frankly quite ridiculous in their extreme. Many chemicals or elements are essential for life, but are poisonous in excess.
For example:
Some moisture is necessary in the nasal passages to prevent dryness. But try holding your head under water and breathing in water for 10 minutes. A silly example I know, but no more silly than the rat poison analogy.
Having said that I do agree that putting ANY chemical in the water supply as a means of dosing that chemical is ridiculous. There is no control over the amount of water consumed and therefore no control over the dose received.
