Theres a lot of opinions out there, but the truth is it depends on your body size, how hard you train, and how much you sweat.
For most lifters, around 1 gallon (about 3.7 liters) a day is a solid goal. If you're training hard, sweating a lot, or in a hot place, you might need more. But drinking 2 gallons isn’t necessary for most people.
Personally, I aim for just under a gallon a day. I drink more if I’m doing a heavy workout or it’s hot outside. Best way to check if you’re getting enough is your urine — if it’s light yellow, you’re good. If it’s dark, drink more. Just don’t force water down nonstop. More isn’t always better.