>>33208627Yes, because any other combination of elements creates different chemicals that already exists. If it's not the same water, then it is literally not water.
Generally speaking, you should assume every rule of a fictional world works the same as the real world unless specifically stated otherwise; considering the fact that the real world is the only baseline we have to on. Otherwise there are literally no rules.
We can assume, since we have never been told otherwise, that water is H2O, the world is round, respiration occurs with oxygen, gravity still works, etc.
Pokemon have literally been described as magic before, so I honestly don't care HOW the water comes to be, but the physical properties of water need to be the same.