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How long could a person of lets say 18 years be able to drink sea water without getting too much into trouble ? Or can a person drink it without noticing that it is a very bad idea ? I don't mean in just 1 drink session but like can one manage a day or two ? Can one drink it and go to sleep and be still healthy (although very thirsty) in the morning ?

(this is just a hypothetical question, I'm not a scientist at all, I'm not sure what tags to use actually)

Additional brainstorming:

  • kidney failure
  • any other organ failure
  • dying of thirst
  • ...
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  • $\begingroup$ I don't remember were I read this. A shipwrecked man drank seawater to stay alive. He claimed that the seawater he decided to drink was to his surprise fresh water. He said that there was a pocket of fresh water floating about on the surface of the sea. Through a recent Google-scan I learned that saltwater is heavier than freshwater. After a a heavy downpour at sea the surface water would be less salty than the rest, wouldn't it? It was said in the article I read that sea water is 3.5 % salty and that the body can just deal with water that is less than 2% salty. $\endgroup$
    – Constantthin
    Commented Feb 24, 2018 at 12:25
  • $\begingroup$ bbc.com/news/world-asia-45623130 This guy did it for 49 days involuntary . $\endgroup$
    – user46257
    Commented Sep 24, 2018 at 12:19
  • $\begingroup$ It takes about 2 weeks under ideal conditions, and as little as a few hours under the worst conditions, dehydration is very strongly affected by things like environment and activity level. Your best bet is to just use information on dehydration as if they were not drinking anything and just use the shorter estimate since sea water is not helping at all. $\endgroup$
    – John
    Commented Sep 24, 2018 at 19:21

2 Answers 2

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(source: free.fr)

Alain Bombard

He is a french biologist who voluntarily tested how many days a man can survive drinking seawater and how?

Biologist point of view

Sea contains ~3.5% of salt$^1$. Our kidney separates the waste from water and excrete them in urine provided the salt content is less than ~2%.$^2$ So, it will take the water already present in the body. Causing excessive thirst and dehydration, eventually cause death.

Alain's Experiment

Just one spoon of seawater at 20 minute intervals, drinking very slowly and letting the saliva in your mouth reduce the saline in the water you have swallowed.

Though he survived 65 days (From and including: Sunday, 19 October 1952 to Tuesday, 23 December 1952, ~4,400km) of his journey and lost 25 kg of weight, this result is never successfully reproduced.

Source:

  1. http://oceanservice.noaa.gov/facts/whysalty.html
  2. http://paradise.docastaway.com/drinking-sea-water
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    $\begingroup$ The results of Bombard, are, nicely said, at least doubted. $\endgroup$
    – Chris ♦
    Commented Aug 8, 2014 at 12:45
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    $\begingroup$ @Chris I think it's more like no one in their right mind believes it.... $\endgroup$
    – user1357
    Commented Aug 10, 2014 at 16:53
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    $\begingroup$ @caseyr547 The accusations agains Bombard where that he was supported (also with food and water) by a ship during his time on the atlantic ocean. $\endgroup$
    – Chris ♦
    Commented Aug 10, 2014 at 16:55
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    $\begingroup$ Bombard had a rain harvesting system on his craft which he drank daily, he was NOT drinking only sea water. By his own admission without rain and fish fluids the sea water would have killed him, the media grossly exaggerates what he did. $\endgroup$
    – John
    Commented Sep 24, 2018 at 19:24
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After drinking 1 liter of seawater with 3.5% salt your kidneys need to excrete at least 1.5 liters of urine in order to maintain normal blood sodium levels, which leaves you with 0.5 liter of negative water balance. This occurs because the kidneys have a limited ability to concentrate urine; it's explained in more detail here.

When a negative water balance results in 1% loss of body weight (0.7 kg in a 70 kg person), which could occur after drinking of about 1 liter of seawater, you can already experience dehydration symptoms, starting with thirst, dry mouth, pounding heart and dark yellow urine, followed by fatigue, dizziness, nausea, headache and eventually coma and death, that can occur at about 10-15% loss of body weight (7-10.5 kg in a 70 kg person), which could occur after drinking 14-21 liters of seawater (Nature.com).

Death occurs due to acute kidney failure resulting in the accumulation of sodium, urea and other substances in the blood.

It is not time, but the amount of seawater that causes problems. One could drink 1 liter of water in the evening, need to urinate several times during the night, and be mildly dehydrated and otherwise "fine" in the morning. But what's the benefit of this?

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