I'm sure that's true, Kevin (and I think wat-ter does rhyme with daughter pretty closely)...but the waitress also dropped the final 'r' and emphasized the 'woah', and then made it pretty clear she was upbraiding the 'ignorant Americans' for their quaint pronunciations...much as the French are wont to do in certain areas and situations.
It IS pretty hard to mistake 'glass of water' twice.