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[Q] The Desert Island salt water question?
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Published by Michaelangelica 04-12-2009
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Definitive and final answer(s?) please
1 I am on a desert island

(No not that type there are no coconut trees-it is a desert)

2.There is limited water one keg of fresh water has been saved from my shipwreck

(No the island is not Australia-will you stop it)
3. There is no more freshwater anywhere

(Yes I tried digging a hole. Please take this seriously)
So the question:-

(No I have no plastic either for a solar still OK?)
How much can I dilute my fresh water with sea water (there is NO GIN!! PLEASE!) so that I survive the longest?
(OK, then assume the barrel of water won't go off. It has a super preservative in it OK-no it won't preserve me!!!~-This could save you life one day you know!!)?
Is this amount the same for young, old, male, female, weather hot cold?
or
What part of the ocean my island is in.
or
If I get the sea water from the top or bottom layer of the sea water?
  #1 (permalink)  
By Racoon on 04-12-2009
Re: The Desert Island salt water question?
In the unlikely event that you find yourself in such a terrible situation, Drink the water from the keg, (presumably in a prudent fashion), and then fill the keg with seawater and find a way to capture the evaporation.

If you can find a way to capture the evaporation/condensation you could repeat indefinitely, and would likely die from starvation and exposure instead of dehydration.

As far as diluting sea-water, that could depend on the individual themselves and how much water the person requires.
A large person needs more water, so the question becomes very subjective in terms of "how long, how much?"
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  #2 (permalink)  
By modest on 04-13-2009
Re: The Desert Island salt water question?
What do ya know, they did a study with rats:
Research on laboratory rats confirmed that drinking sea-water when dehydrated, was not beneficial and caused impaired renal function. When the concentration of sea-water in the drinking water is gradually increased there is a gradual increase in water uptake and corresponding urine excretion. At 50% sea-water the maximum uptake and excretion is reached. Following this there is a decline in appetite, water uptake and urine secretion. When on 100% sea-water, the creatinine clearances were greater than on tap water, while urine/plasma osmolalities (U/P) averaged 7. The only higher U/P was found in animals drinking sea-water when dehydrated, i.e. a U/P of 11. The urea metabolism appears to be suited to either the need to conserve body water, up to 50% sea-water, or to guarantee an adequate urine production, from 50% sea-water to pure sea-water. It is suggested that when a man is stranded at sea it is not advisable to drink all the fresh water and then be compelled to drink sea-water when dehydrated. It is better to slowly increase the sea-water uptake. This will prolong the time before sea-water needs to be drunk and result in only minor metabolic changes. Return to fresh water will be followed by an immediate return to normal homeostasis.

Metabolic effects in rats drinking increasing conc...[Comp Biochem Physiol A Comp Physiol. 1987] - PubMed Result
So.. step 1: don't mix the fresh and salt water in the keg. There's no need to introduce bacteria and whatnot in the keg. If you don't have a smaller container to mix them in then just drink them in small amounts alternatively. Step 2: never more than 50% seawater intake. Step 3: slowly increase the level of seawater (presumably from 0 - 50% linearly for as long as the freshwater is going to last) which might require a bit of calculus. If you don't know calculus... well... sorry, you're gonna die

~modest
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