Why risk being dehydrated and injuring yourself, or not get a good workout in because you feel like shit? Your body will let go of whatever water it doesn't need, and water is cheap so it's not like your wasting money by drinking more than you need. If your urine isn't clear, and your not going to piss every 30 or 45 minutes your not drinking enough. You should be drinking water like you eat, drink before you are thirsty and the more you drink the better. Some people say two gallons, some say one, whatever works for you just be sure to do it. I personally drink two, but I also do more cardio than most people on top of my gym routine.