5 to 6 litres of fluid a day is enough. During winter a bit less, during summer a bit more, it could reach 2 gallons.
It's not that much, just spread it. In the morning two glasses,
before sleeping two glasses,
during training half a gallon, other types of fluid like tea, two cups, some orange-juice, about 2 glasses, during supper I drink something, and so on.
BTW,
I weigh well over 250,
if you weigh less, you could accomplish the day with less.