i would challenge anyone to try drinking a half gallon of water, when the body has all but 'closed up shop' and is getting to work on some deep issues, while keeping guard over all the balances that need be maintained.
No matter how much of a water drinker you are (and I was, before my water fast), there comes a point at which the body doesn't want (much) water. By the same token though, I do not support the practise of denying oneself water, out of some heroic concept of dry fasting, especially in the early days.
To everything, turn turn.
After twenty one or two days, I was pretty much down to 12 ounces-- or less. There's a good reason for rest on a water fast. It allows the body to do some pretty amazing, largely invisible and under-appreciated work.