From the Letters to the Editor (we should, apparently, be concerned that most people don't know the form of fluoride in our drinking water...)
All these people think fluoride is a benign constant, but as soon as you rearrange a molecule or add an atom, you have completely different properties. Everyone with basic chemistry knowledge should know that.
Let's do a little lesson here: O2 = air, H2O = water, H2O2 = hydrogen peroxide, a powerful bleaching product. All these chemical substances have oxygen, but are totally different products. Back to fluoride: there is calcium fluoride, sodium fluoride which is mainly used in toothpastes, and hydrofluorisilicic acid, a grade 4 chemical hazard.
The letter ends with a cry for the various authorities to 'stop forcing us to drink hydrofluorosilicic acid.'
First up - & you may well think I'm being a pointy-headed pedant on this one - O2 isn't 'air', It's oxygen, one component of the atmosphere, albeit a rather important component from our point of view. (The discovery of the element oxygen is credited to the English scientist & polymath Joseph Priestley, although the Swede Carl Scheele actually beat Priestley to it by at least a year. However, Priestley published his work first, leaving Scheele out in the cold. This site has a couple of brief videos about the early work on oxygen, which also involved Antoine Lavoisier. You just have to sit through the boomdeyada song first! Each time you want to watch a video - they really ought to fix that.)
Anyway, back to the chase. Unfortunately for the argument presented here, fluoride is a constant - the different molecules listed have forms & properties dependent on the combination of atoms they contain, & how strongly (or otherwise) those atoms are linked together. Oxygen remains oxygen, regardless of the atoms it's combined with. (And incidentally, H2O can be pretty dangerous stuff. A number of people each year are killed or injured by dihydrogen monoxide, in its liquid, solid, or superheated gaseous states...) Hydrogen peroxide is highly reactive because of its chemical structure - the bond between its two oxygen ions is unstable & easily broken. Incidentally, while drinking the stuff would not be a good idea, hydrogen peroxide is produced in your body as part of normal metabolic processes, although at much much lower concentrations. So concentration is important, isn't it?
Which is a key point about the source of fluoride in drinking water. Even if we were drinking hydrofluorosilicic acid, the quantity we'd be getting is so diluted as to be harmless (in the acidic sense). But we're not being forced to drink hydrofluorosilicic acid, which dissociates in water to release fluoride ions, not an acid. (The issue of whether or not fluoride should added to the water isn't the focus here.) Thus the letter makes an invalid link between the hazardous nature of concentrated hydrofluorosilicic acid and fluoridated town supply water - while this may well be a common debating trick it's definitely not good science. In addition, water treatment includes balancing the pH of the town water supply - you can rest assured that what comes out the taps is most definitely not an acid :-)