Ok.. there are 2 components to what I'm talking about
Physical: That's mainly what I wonder - can you change the body?
Mental: By practicing regular periods of tolerating thirst beyond the point where you'd normally drink you can cultivate the ability to hike further than normal without water and without as much mental distress You're not *really* going to die - you're just torturing yourself mentally for 2 hours until you get to the water. THAT is what I'm talking about - the not torturing yourself mentally part.
Very similar to marathon training. If you're working up to 20+ mile runs you have to run through discomfort that make someone who isn't training immediately stop. Yeah, it might be what the body wants but you'll never run a marathon that way.