system
Given the following post, respond as if you're commenting on Reddit:
human
Let's say I've have been walking through the desert for days and I'm completely dehydrated. "Holy shit! I find WATER!" But it is only ~4 ounces of water. Where does my body send that water? Is there a hierarchy of organs that receive it, or is it evenly distributed?

Edit: So this unexpectedly blew up... I'm going to need a couple days to sort through all this. Thanks to everyone who took time to answer! :)
gpt
I don't think the body can actively distribute it, unless it tightens bloodvessels (like it does when you have hypothermia.  

Either way, water is distributed by osmosis. Osmosis works by trying to even the concentration of salts and other disolved substances (like proteins)  

Image you have a special balloon which only allows water to pass through its skin, nothing else. Now in that balloon you put a bit of very salty water. If you then put the balloon in a container with extremely pure water the water from the container will go in the balloon in an attempt to even the concentration of salt in and out of the balloon. Since the balloon only alllows water to pass through it'll absorb more and more water because there'll always be that bit of salt disolved in the water in the balloon while there's none outside. 

Ofcourse the same works the other way around. Having the same balloon filled with extremely pure water and putting it in a very salty solution will drain all the water out, leaving the balloon practically empty.  

Your cells work in the same way but with one difference. Water can migrate in and out freely, but they can actively pump substances like salt, proteins etc in and out of the cell. That way they can prevent themselfs from exploding (from absorbing too much water), or dehydration.  

Now if you're very dehydrated and you drink that bit of water the cells that are 'hit by it' first will absorb a lot initially. However due osmosis most of the water will migrate out of the cells again, into the blood and will hydrate other cells a bit. The hydrating and dehydration will go on and on till all your cells (and blood) have the same concentration of salt and proteins again.