ORIGINAL: loughbd
"some waters"? I only know of one kind of water. It is made from two hydrogen atoms and one oxygen atom combined by a covalent bond.
If you'd take the time to read that link I provided above you'd see that we were wondering about the affect of the various dissolved metals, salts, fluoridation etc of tap water and how the heat at boiling point may activate them to discolour the surface. Don't give lectures when you don't know what we were talking about.