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If water has a low salt content, it hydrates us. When water has too high salt concentration, like sea water, it drains water out of us instead when we drink it. At what salt concentration would water leave us completely unaffected?

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  • $\begingroup$ given the coment from anongoodnurse here biology.stackexchange.com/questions/24058/… - the answer is 'there is no such concentration' $\endgroup$ – AliceD Jul 2 '15 at 14:02
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    $\begingroup$ @AliceD Thanks for your comment, I didn't come across that question before. However, I don't really agree with the given comment. $\endgroup$ – Nit Jul 2 '15 at 15:04
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    $\begingroup$ As I said before, if you're not dehydrated, you cannot "hydrate" with a perfect imaginary solution. The body will remove the unnecessary salts of anything added. There is no magic "solution". better to disagree with me by posting a better answer; at least then you will understand the physiology behind it. $\endgroup$ – anongoodnurse Jul 3 '15 at 1:05
  • $\begingroup$ water leave us completely unaffected Haha!!! this sounds like you are attempting to recycle water without any other recycling material :P $\endgroup$ – bonCodigo Jul 3 '15 at 7:02
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    $\begingroup$ The short answer is that anongoodnurse and moose are correct. The long answer is study physiology. Even when water is isotonic to blood, the composition of it's ionic species differs. Blood contains a wide variety of dissolved proteins, metabolites, and minerals. Na and Cl are major constituents, but are not the only components whose levels are carefully regulated. Your body corrects for the changes in the concentrations of these molecules. Even if you transferred blood which happened to have the same composition, your body also regulates volume and would need to make adjustments for that. $\endgroup$ – InactionPotential Jul 3 '15 at 15:20
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"Unaffected" is impossible. If you meant homeostasis, where fluid ingested = fluid excreted, well that happens all the time, and all "output" is not through urine. Sweat, respiration, fluid in feces, etc. are fluid loss. The body constantly needs water. Fluid regulation is a highly complex system managed by the body through a variety of osmotic gradients in the body and hormones which is not driven solely on the osmolarity of the fluid ingested. Under no circumstances would fluid ingested pass through the stomach, small and large intestine, and colon without absorption. Once absorbed from the GI tract to the bloodstream, our kidneys regulate fluid balance. For more reading, reference the renin–angiotensin–aldosterone system.

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    $\begingroup$ +1 "Fluid regulation is a highly complex system managed by the body through a variety of osmotic gradients in the body and hormones which is not driven solely on the osmolarity of the fluid ingested." $\endgroup$ – anongoodnurse Jul 3 '15 at 1:02

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