i don't have a number for you, but my cousin once told me about a guy he knew that drank so much water every day that he had to be hospitalized becuz he literally washed all the nutrients in his body away and he became sick. i just know that as a minimum, you're supposed to drink 4 quarts (1 gallon) to stay hydrated. start adding massive amounts of food to that and especially supplements and i really don't think 2 gallons would be dangerous, depending on your size and what/how much you're consuming. just remember these words: CLEAR AND COPIUS(sp?). that means you should be drinking enough water that your piss is clear and there's a lot of it. i know vitamin C can turn piss orange, but i dunno if you're drinking lots of water if that will make a difference.