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The Great Outdoors

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  • No worries. I had good intentions. All good.
    – Ken Graham
    Commented Oct 27, 2019 at 13:01
  • You mentioned the heat acclimatization, which increases sweating and therefore the water need - I'm not sure if I can read this from your answer, but you might want to emphasize it, because the OP is asking about how to decrease the water intake. Then, plasma volume increasing by 2-3 liters sounds highly unlikely to me, knowing that the average blood volume is about 5 liters. You might want to just skip that, because it may not be relevant for this question, anyway.
    – Jan
    Commented Oct 28, 2019 at 9:57
  • @Jan: Increase in sweating, need for more water: I had meant that to be the recurrent theme of my answer. Still, I tried to make it even more clear. Plasma/body water: you're right - I corrected/clarified the answer: the 2-3 l increase is in the total body water, plasma expansion would be around maybe 1 l (still a lot). I do think it relevant as this effect alone gives more of a "heat buffer" than than what could be saved theoretically by the kidneys completely shutting down plus using the heat capacity of the human body to increase body temp to 40 °C (heat stroke temp) together.
    – cbeleites
    Commented Oct 29, 2019 at 15:02
  • @cbeleites, you may just want to skip that "plasma volume," because it is a bit confusing and unnecessary, but the total body water and the entire point of your post is just about right.
    – Jan
    Commented Oct 29, 2019 at 15:07
  • @Jan (edit is back) re need to total more water, I'm not sure. It is clear that we gain the ability to sweat more (sweat rate) and thus increase the output in physical power, plus to endure that power output longer. But for the same physical work done during the same amount of time - I'm not so sure. Lower onset temp and higher sweat rate would suggest more total sweating. But sweating is regulated to get rid of excess heat, so if there no more excess heat, total sweat volume may not be increased. I didn't see study results on this. (Personally, I regulate my power output by sweat rate...)
    – cbeleites
    Commented Oct 29, 2019 at 16:44