Formula of water is always H2O, except with the "heavy" water, used in nuclear experiments, where after the process it reaches H30, regardless its aggregate state.
Are you sure of this? To my knowledge, heavy water and even tritiated water still have the same molecular formula: H2O, though you'll often see heavy water shown as D2O and tritiated water as T2O. However, I don't think you'll ever see it as H3O, as you claim.
In essence, the number of atoms in the molecule of water never change--you'll always have two hydrogen atoms and one oxygen atom. What is different is the isotope(s) of the hydrogen atom(s) contained in the water molecule. ALMOST all hydrogen atoms contain only the one proton with no neutrons, but nature provides us that one rogue hydrogen atom out of so many thousand that also possesses a neutron. We call this form of hydrogen deuterium
, the hydrogen isotope seen in heavy water (D2O) or semi-heavy water (HDO). Add another neutron to the nucleus of the deuterium atom and you get a radioactive hydrogen isotope known as tritium
, which is most often one of the byproducts of nuclear experiments (or nuclear energy production), but can be found in nature in trace amounts.
Again, however, a water molecule will always have the molecular formula of H2O, otherwise it wouldn't be water at all. This is true regardless of the hydrogen isotopes contained in the water molecule.