>>9856170it actually depends on the chemical reactions, your body tries its best to reuse resources as much as possible and most (but not all) of the reactions use water as an intermediate but end up reforming it. the number of hydrolysis reactions usually equals the number of dehydration reactions more or less so your net use usually ends up being the same, and if that was the only factor you'd hardly ever need to hydrate
the problem is your body produces waste products that it is unable to keep using and often is toxic if it builds up, and the solution your body has is to dissolve it all in water and release it. that's why you have to keep hydrating
here's a weird fact though: humans and i think chimpanzees are the only mammals that need to have vitamin C as part of our diets: the rest can produce it on their own, and it's a critical part of metabolism so it's odd that there would be a loss of a trait that would be so important. it's believed somewhere down the line in our common ape ancestor, vitamin C was so naturally prevalent in the animal's diet that when a random mutation that prevent synthesis occurred, it didn't affect the survivability of the creature because he was getting enough anyway. that one random mutation happened to be the one that got passed down to us, and we didn't even realize that until our diets shifted with civilization and people started getting scurvy
