I have a tendency to cramp, so I usually drink water right after I weigh-in, so I won't get completely dry and cramp at the end. But I don't drink much, probably 4-6 ounces at the max. I always have a bottle of water available after dialysis in case I cramp on the way home. Water usually fixes the problem, although not without a few minutes of pain.
I see dummies drinking coke during dialysis's all the time