That actually sounds like a lot of water, and I am a person who tends to probably drink, when I eat, about eight cups a day.The idea some have that drinking more will make everything go faster is quite innacurate. It puts more strain on the kidneys, for one.
most of the old fasting literature, where the masters fasted thousands, says: "drink only according to thirst"
Naturally, (though we might forget this), they tended to fast people and REST them.
They were not trying to lose weight, nor to exercise it off, at the same time. They were mainly concerned with rebuilding a body, and letting it rest and attend to itself.
Many today are primarily concerned with how much weight thay have to lose--and it is true that the more you have, the longer you can water fast--in theory. I have a sense some of the people who push with the exercising thing while
Water Fasting are setting themselve up for a crash.
as to what to expect, please read the literature! Google "soil and Health" in this forum,or google "chrisB" and "stages of fasting".
best C
PS--just wanted to add, your weight does not preclude you fasting for 20 days, or more if you find it goes well. You will lose less if you have less to lose--also, what you lose will be recoverable: your own sensations can be your guidance system. Many times people have water fasted and been skeletal at the end--Because they were ill and low-weight to begin with--and have come back beautifully, with systems that function!
This is one reason to go into retreat mode and stay away from those who are frightened by appearances--and a good reson too, to read the great material that's out there. Soil and Health has the best lit, and it's free.
PPS,
Have a wonderful fast!
I loved my first water fast, ups, downs and all. (29 days)
It changed my life entirely. (mainly my mind, but the body too, and I continue to get better and better.)