I always drink 1+ gallons. I buy a gallon jug just to drink at work in a 8-10 hour period. That way I 100% sure i have a gallon plus. That is off cycle. On I drink much more so I know I am flushing my body completely.
the rule of thumb is .45 times your body weight in ounces is what a person should drink on a daily basis to maintain good health. Of course you can never get too much water...but like all the guys said a gallon or more when cycling is more than enough to keep the body cleansed.....