How long animals can last without water very much depends on the animal, says Stuart Blackman <\/p>
Water is utterly essential for Earth-based life-forms. This simple compound, made of oxygen and hydrogen atoms bound together in a two-to-one ratio, has been present on our little blue planet for at least as long as life. <\/strong><\/p> A powerful solvent capable of dissolving a multitude of other molecules, it\u2019s an ideal medium for the complex chemistry required for biological systems. Most of evolutionary history took place in water, and it remains the main ingredient of animals\u2019 bodies \u2013 95 per cent of a jellyfish<\/a>, for instant and 60 percent of a human.<\/p> No animals can survive without water. Tardigrades, or water bears,<\/a> probably come closest. These tiny invertebrates can tolerate losing 99 per cent of their water content by entering a state of suspended animation, during which they can also survive extremes of temperature, pressure and exposure to radiation. Experiments have shown that they can endure for up to a decade in this dehydrated state.<\/p> Most animals, though, must keep their water levels topped up. On a wet planet such as ours, that\u2019s fairly straightforward for many species. But, where water is scarce, the challenge is as much about not losing water as it is about finding it \u2013 especially challenging when it\u2019s both dry and hot. <\/p> The higher the temperature, the greater the rate of water loss by evaporation through the skin and via the breath. And sweating to cool down only exacerbates the problem, which is why a human wouldn\u2019t last much more than a day in a desert without drinking. <\/p> Little surprise that hot, dry specialists such as camels tend not to sweat at all. To compensate, they are able to tolerate a rise in body temperature to 42\u00b0C (five degrees higher than humans). Only the most heat-sensitive tissues of the brain must be kept cooler. This is achieved by collecting the moisture from exhaled breath in the nasal passages, from where it evaporates when the animal inhales, cooling the blood<\/a> supply to the brain by 4\u00b0C.How long can animals survive without water?<\/h2>