You should be drinking upwards of 128 oz of water a day now as it is... 64 oz isn't even enough for a human normally. (not counting other "water" sources) right now the recommended minimum is around 100 oz.
I always stress pushing for 128 oz, for several reasons. First and foremost, your body needs the water. Secondly, fat is water soluble, and requires water above your daily needs to most effectively process the fat removal. It's not as hard to do as it seems, it just takes changes in your normal habits. Keeping a bottle with you at all times and actually drinking it, helps.
Will you die... eh, you'd get really sick and end up in the hospital before that happened, unless you just totally ignored all the dehydration warning signs.
But still, don't stress about things just work at making changes slowly. Not everyone can just start magically being able to consume 128oz of water a day, you work up to it slowly.
So... start now, get that habit fully "stuck" before surgery.