We're about to go on a journey into the wild and exciting world of chemistry... Get ready, because it's going to be awesome... First of all, let's look at what they're putting in the water. The active ingredient is the fluoride (F-) ion. Now, generally ions don't occur on their own, and fluorine is extremely electronegative, so it really wants to ionically bond with something, so you're probably going to use a salt like sodium fluoride. Now, this is fine, because when you dissolve it into water, it dissociates into sodium (Na+) ions and F- ions. Now, if you've been keeping up, then you might note that sodium is a metal (not a heavy metal, but still a metal). Now, that is true, but you are thinking of metallic sodium, which is not charged, and if it comes in contact with water, then it would catch on fire. Na+, on the other hand, doesn't really do anything. In fact, in an aqueous solution, it will never bond with anything. If you know how atomic bonding works, then you probably know that mots atoms in the same column bond similarly. Well, if you notice, fluorine is right above chlorine. Sodium chloride is a pretty common compound, more commonly known as table salt. Well, it behaves almost exactly the same way as sodium fluoride. So there. Now, to reiterate the accusation that sodium fluoride is a heavy metal, well, first of all, compounds (and ions) never behave as metals, and furthermore, heavy metals are metals like lead and barium, and not sodium. And fluorine isn't even a metal. It never behaves as a metal. Even if you ask nicely. Now, the corporate accusation is ridiculous because it's a city matter, and the government is by definition not a corporation. Most countries have not banned it. The few that discontinued it discontinued it because they started using fluoridated salt (we usually use iodized salt, so we have an extra halogen ion just for fun). They did not discontinue it because it causes cancer, because it totally doesn't. See, whenever people don't like something, they say it causes cancer, because they're relying on the fact that most people don't know how cancer works. See, most cancers come from free radicals, which are basically single electrons. Electrons really dislike traveling by themselves, so they pick up pairs whenever they find them. So if they steal an electron from your DNA, then that causes it to basically freak out and start replicating incorrectly like crazy (or something like that). Now, not only do both sodium and fluoride not have free radicals, their ionization energy is ridiculously high, and they have no electron affinity. So I fail to see how it has anything to do with cancer. As for calcification, in general, you actually need to have calcium to cause calcification of anything. Past that, conspiracy, conspiracy, crazy. So ya... That's why chemistry is important, children!