>Same way they can expel a volume of water bigger than their bodies in a single attack.
Pooolease, anon, that you learn in elementary school.
Who was your pokemon professor?
Was that hippie Birch?
Pokeballs probably put a device in the gills that filters air to only let as much as they would get from water in. Also makes them levitate, but only a tiny bit.
They use minor teleportation magic to take water from somewhere else.