I'm a 33 year old male. Because of my work schedule, I can work out only two days in a row, then rest for two days.  Generally I drink about 64oz of water on the days I do weights or cardio.  The days I work, I usually drink a little less.  I don't want to gain a bunch of water weight, but I want to stay hydrated.  Is their an amount of water that I need to drink on workout days opposed to resting days? Or is 64oz a good rule of thumb to stick too.