IMO, since they're built to survive space, plasma burns, focused laser beams, missiles, explosive bolts, Napalm-X and being hit by a 20-foot long marriage of a chainsaw and a sword... Water wouldn't really be an issue. Although this is more of a thematic question that Joseph would be able to answer; as he created the mythology for Gearhead, he'd be the one to answer if a Buru Buru is waterproof or not.