Pokémon seem to be exceptionally good at turning matter into energy and vice versa. However, at some point, a Vaporeon needs to eat. So not technically infinite.
I am aware, just assuming that the Vaporeon itself is constantly fed / rehydrated, which considering it's a water pokemon and not a plant it probably doesn't wait around to receive sources of water like Leafeon may. But a grass type would be much more wise not to bite a paw that could continuously feed it so to speak.
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