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Drinking sea water can be deadly as it contains too much salt, basically de-hydrating the body. Normal tap water contains little salt and is good for re-hydration. My question: How much salt needs to be dissolved in water such that it does not hydrate nor de-hydrate? For instance, would a physiologic saline solution (9 grams of salt per liter of water) meet this criterion?

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    $\begingroup$ You are looking for physiological saline which is isotonic to most tissues. It is about 0.9% w/v, which equates to ~9g NaCl per liter water. $\endgroup$ – kmm Nov 16 '14 at 17:25
  • $\begingroup$ @kmm I thought isotonic solutions were often used in sports for rehydration? $\endgroup$ – AliceD Nov 16 '14 at 23:26
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    $\begingroup$ @anongoodnurse Why do you say that? There are solutions that can be isosmotic with the cytoplasm. I agree that the cytoplasm can have small variations in osmolarity and you may not find a mathematically exact universal isotonic solution. Why do you think 0.9% saline won't be grossly isosmotic? $\endgroup$ – WYSIWYG Jul 2 '15 at 14:44
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    $\begingroup$ @anongoodnurse That still makes no sense. What about solutions that are perfectly balanced between the body-needs-solutes and body-doesn't-need-solutes? $\endgroup$ – Etheryte Jul 2 '15 at 23:13
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    $\begingroup$ @Nit Oh sorry.. there was a confusion. I thought you asked anongoodnurse to read about loops of henle etc. Sorry. However you have to work on your other question- on terminologies and w.r.t addition of your own analysis on the issue. $\endgroup$ – WYSIWYG Jul 3 '15 at 9:18