Just to be clear, the vapor emitted from an e-cigarette is not water vapor. Water vapor is invisible. The vapor from an e-cig--like clouds, steam, fog, etc.--is liquid vapor. Invisible water vapor condenses to form liquid vapor, which then dissipates and returns to its original state as water vapor. So it's a circular process. Nothing new is being created and nothing is going away. Basically, we're just messing with the molecules.