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Just out of curiosity, consider the following situation. I'm going to die out of thirst and there is no source of water, but sea water.

Should I drink it? OR it will just make things worse and make me more dehydrated?

In other words, at which point should I consider drinking, maybe just a small sip?

Please reply according to scientific facts or true experience.

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In the attempt to prevent or treat dehydration you should not drink sea water.

In short: By drinking seawater you ingest excessive amount of sodium chloride, which needs to be excreted by urine in order to maintain normal blood sodium concentration. Since the human kidneys have a limited ability to concentrate urine, the amount of water lost by urine in order to excrete sodium chloride is greater than the amount of water in the drunk seawater. This results in a net water loss.

Detailed explanation is below:

E. Hall, Guyton and Hall Textbook of Medical Physiology, 13th edition, 2016 (p. 373)

The limited ability of the human kidney to concentrate the urine to only 1,200 mOsm/L explains why severe dehydration occurs if one attempts to drink seawater.

Sodium chloride concentration in the oceans averages about 3-3.5% with an osmolality between about 1,000 and 1,200 mOsm/L.

Drinking 1 liter of seawater...would provide a total sodium chloride intake of 1,200 mOsm. If maximal urine concentration ability is 1,200 mOsm/L, the amount of urine needed to excrete 1,200 mOsm would be...1 liter.

The kidneys must also excrete other solutes, especially urea, which contribute about 600 mOsm/L when urine is maximally concentrated. Therefore the maximal concentration of sodium chloride that can be excreted by the kidneys is about 600 mOsm/L. Thus for every liter of seawater drunk, 1.5 liters of urine volume would be required to rid the body of 1,200 mOsm of sodium chloride ingested in addition to 600 mOsm of other solutes...This would result in a net fluid loss of 0.5 liter for every liter of seawater drunk.

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    Interesting answer. Thank you. Could you add some references for your first part? And maybe also add the reference (Textbook of Medical Physiology - Guyton and Hall) provided by the author of the answer you are linking to. Tbh, I am not sure your question is really "original" as it basically links to a similar question (and answer) of another Q/A website... Cheers! Felipe! – Felipe Sep 17 '16 at 12:47
  • @Felipe My first part is just a more plain-language summary of the quoted part. I believe that, in principle, the answer is correct, but someone could argue about the exact resulting extent of negative water balance. Again, I searched for other online references and I didn't find them. Pointing to offline physiology books here makes no sense for me since it's not practical for readers to check them. – Jan Sep 17 '16 at 13:40
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    _I believe that, in principle, the answer is correct, but someone could argue about the exact resulting extent of negative water balance. _ So why are you linking your answer to this 3rd party site answer although you are not convinced of it? And I still think you should mention the source the author of the "original" answer. Someone might ask, where do those number come from? There a many review on the topic, so you should be able to find one. As you suggested you are a MD, I think you should keep the standard of your answer on health SE with the same standards you apply for your work. -1 – Felipe Sep 17 '16 at 14:54
  • I found an explanation from the Guyton and Hall Textbook of Medical Physiology. – Jan Sep 17 '16 at 17:22
  • Ok thanks. Your answer looks much better now. +1 Cheers – Felipe Sep 20 '16 at 17:44

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