Miles, are you getting white smoke out of your exhaust pipe? If not, other than noticing its using water, what other signs or symptoms are you having? I'm having the same problem of using water but not nearly to the degree that you are. I may need a valve job and a new head gasket (already did the head gasket once; didn't help). I'm unsure where to turn myself. Have retorqued the head bolts a couple of times; no improvement.
Mike