Just one opinion, i believe we need considerably more water early in the fast (perhaps the first 3-4 days) to help eliminate the large amount of toxins and considerably less water after that. I would drink in the first 3-4 days about 1/2 to 3/4 ounce or so per pound of weight ie: if 120 pounds, then 60-90 ounces of water which is 7.5 -11 cups.
After this i would drink primarily according to thirst which would likely amount to 2-4 cups per day of sipping.
It should be the purest of water and ideally distilled.