How Much Water to Consume In One Day?

Found a site that said that you should drink one FULL gallon (16 8oz cups?!?) of water a day. More so (20+ cups????) if you're overweight? Isn't that just a -wee- bit much of water to consume in one day? I mean, given, yes, you're not eating anything, but still, that just seems like a lot. So is there truth to it or not? Considering my weight (last time I checked, I think I was 270 pounds), should I stick to 8-10 cups of water a day or should I do more? How large an amount of water, generally speaking, do you guys consume in one day?