Everybody's body is unique and we differ in our ability to do this. PCT Thru hikers often speak of "cameling up"--guzzling as much water as they can handle in the morning and at rest stops, especially in the Mojave and in NoCal-SoOre where distances between reliable water are huge. Certainly, anybody who's made it from Mexico to the Oregon border has their system fine-tuned and are probably processing water very efficiently. The dry air helps, too (I hate hiking drenched in sweat that won't evaporate).

Back when I ran I was able to run distances in heat with only an occasional drinking fountain sip or two during--I prefered not having water sloshing in my stomach while pounding the miles. Nowadays folks seem to pound gallons on the go (you kids, get offa my lawn). Even when cycling I don't drink all that much, although in the heat there's nothing that dehydrates me faster (icewater in insulated bottles has helped me keep up).

Backpacking is different than those sports for some reason, and I drink on the go and seldom stop for replenishment, unless it's a long day. That's the Sierra and in stark contrast to the Cascades and Olympics where we'd just scoop and drink on the go (with the ironic Sierra cup). Boy, do I miss not lugging pounds of water.

Cheers,

Rick