You've got that from the UU strategy section, haven't you? It depends on the tier you are going to use it. There are only two notable Pokemon in UU you might hit with that, Rhyperior and Rotom-H. Because Galvantual doesn't have many options anyway there is nothing wrong with Water - especially since Gastrodon ascended tiers there is no use for Energy Ball anyway.EDIT: And a question of my own: how viable is Hidden Power Water Galvantula?
In OU/Uber you pretty much want to use Ice to make short shift of Landorus and probably some dragons.