How? How do you get in all of the liquid into your little stomach?
Part of our problem is that we don't know the meaning of a sip or a tiny bite :-). 64 oz. of fluids is NOT a lot of fluid. Many if not most of us consume much more fluid than that in the course of a day without realizing it. It might not be in water, but it's in fluid.
You don't have to drink it all as water. It should be calorie free, caffeine free and non carbonated, that's all.
I wasn"t able to get a lot of water right away but I did have quite a few sugar free popsicles and sf jello instead. I was never a water drinker pre-op so I did worry a bit about getting dehydrated but it didnt happen. I know food has water in it too and I did have soups & chicken broth and anything else I could get down. I made it. Just keep at it with water or substitutes in the beginning. . . it may be a small stomach but it keeps emptying so you must keep filling it . .