Heard somewhere it was an extra 8oz for every lb you wanted to lose. So I figure if I fill the bathtub up in the morning and have it gone by the end of the day I should be good. Of course, I'll have to have it gone by the end of the day because I'll have to sleep in the bathtub because I'll need to be in the bathroom all night!
I like to drink water luckily, so it's not that hard for me to drink it. But like Heather said, you get liquids from other stuff that you drink too (coffee, tea, fruit, etc.). I think as long as you are making the effort to get more water in, and try to aim for the 64oz that Sidrah mentioned, you should be fine.