i bring 2 nalgenes to school every day they come home empty every day then i usually go back and forth from computer to sink to bathroom to computer, just refilling it, ends up some where near 10 to 15+ liters aday.
1-2 gallons a day is the range you should shoot for. whats that your say? 2 gallons is too much, it could hurt you. well this is not true it's more around 3-4 gallons that will cause serious problems, and get you hospitalized. so drink up