I honestly don't know the answer to this but it's something I've always done and wanted to toss it out for discussion.
Before I hiked so often I ran a lot - marathons, a few ultras, and more half-marathon and shorter races than I can count. One of the things I did when I was training was purposely not drink water thinking that my body would acclimate to not getting fluids in a similar way that it acclimates to climate.
I do that still - I walk a lot (5-10 miles a day) and never carry a water bottle. Many times I get very thirsty and instead of stopping at a fountain or walking by a store I'll tough it out for the last few miles.
So... my question is - do you think you can train your body to get by with less water by toughing out thirst for a while? Or is it more a psychological thing where you just build the mental stamina to push on even though you're thirsty?
Note I'm not talking about being stupid and falling out from dehydration.. I'm talking about just pushing a bit past the comfort zone....