He's always drinking water. Before his cooking lesson with Clemenza. On the train. With Fredo while Fredo has a banana daquari. At the meeting with Batista.
Well, you've got a point there...any character seen excessively drinking water (or club soda) at least FOUR times, in two movies covering a 13 year timespan has GOT to be interpreted as 'pre-diabetic'!!
He does ask Al for cold water upon returning from Cuba...I'm not sure if he drinks any, just soothes his eyes. But still, he ASKS for the water...does that count? I think it should.
What about the deleted scenes...we've GOT to see if Michael's drinking water (or club soda) in any of the deleted scenes because just anything we can find will further prove the theory!!!
(By the way, weren't there pitchers/glasses of water in front of most of the attendees at the Batista meeting...as there would be a almost any similar gathering of businessmen in a boardroom? -- Another thing I'll have to check out during next GFII viewing.)