In Frank Herbert’s Dune, the desert-dwelling Fremen conserve water by wearing the “stillsuit,” a jumpsuit of some waterproof material which collects their sweat (and urine) for filtration and re-consumption.
Very clever. Why don’t they die of heatstroke? Sweat isn’t just one of nature’s little design flaws, like zits and ingrown toenails. Sweat is how your body cools itself: Evaporation is a cooling process, basic high-school bio. When your sweat evaporates, it takes some of your body heat with it. Pigs wallow in mud, cats lick themselves all over, dogs pant, because they can’t sweat and they need to cool themselves some other way. If you’re a human, and you’re wearing a waterproof suit that keeps your sweat from evaporating, and you live under a desert sun . . . you get the idea?
BTW: The stillsuit apparently does nothing to stop the body’s loss of water through respiration, which is significant – just breathe on a mirror and watch it fog.