ONCE again the nonsensical idea gets an airing that fluoride is poisonous and adding it to our drinking water will have all sorts of horrendous consequences.

Let me therefore reassure any readers concerned by M Watson’s (HAS, July 8) irresponsible statements that fluoride is perfectly safe and harmless and in fact quite beneficial.

The idea that it’s poisonous seems to stem from some people’s inability to distin- guish it from elemental fluorine, and – yes – that is undoubtedly poisonous.

To set the matter in context we might refer to concerns that have from time to time arisen about a related chemical (they both belong in group 17 of the periodic table) – chlorine. Chlorine is extremely poisonous but not as its negative ion – chloride. In this form we most commonly encounter it in table salt (sodium chloride).

As such it’s not just pleasant and harmless (alright go easy on it if you have high blood pressure), it’s actually essential to our survival.

True, fluoride may not necessarily be an essential component of our diet, but it is a perfectly harmless and quite helpful one.

Tony Kelly, Crook.