It depends what you eat. If you just eat juicy fruits you can probably not even drink any water (unless you sweat out a lot throughout the day, etc). If you eat heavy and/or dry food you should drink until you feel satisfied. I would start drinking 15 minutes before eating and then follow drinking 15 minutes after eating until you feel content. Your body will tell you when it is satisfied.
I do 30 hr dry fast then refeed. I start with ginger and honey in about 24oz of water as this helps my body to relax and also helps to restart the gallbladder. After my meal I drink about another 50oz within 3hrs ending with half a teaspoon of baking soda in it. Then restart my fast.