Last Airbender fan too?
Yeah, those elements make sense for those houses. Though still shocking that water is associated with Slytherin as that element represents love, family, healing and life in most cultures. Actually, no. Now that I think of it, Salazar Slytherin's "pureblood obsession" is an incredibly twisted version of concepts like love and family, so I guess the Slytherin waters are poisoned with intolerance (represented by the Basilisk living in the constantly flooding Chamber of Secrets).