I have done that and it def makes me feel relaly light headed I think it depletes your electrolytes....if your doing a fast longer then 3 days I'd say no but I"m sure other will tell you not to do it at all...
so , out of curiosity, what were your goals when fasting? what were you trying to accomplish? mine is going well... im on day 2 of a 3 day fast. However, its going well enough that i think i might keep going for a bit. maybe for a week. We'll see. this is my first water fast. I plan on going to raw foods when i am done too.