In recent news reports that all seem to be saying the same things:

The teenager only had a few days worth of supplies and survived by catching fish, burning wood from his hut to cook them, and sipping seawater through his clothes to minimize his salt intake. (emphasis added)

Other reports mention running out of cooking gas for a small stove, and a week's supply of water.

Question: Is there any known technique to survive by drinking sea water for many weeks "desalinated" using clothing?

I can imagine using wet clothing as a cooling mechanism for use in a solar still, but I'd never heard of using clothing as a filter. I'm thinking that the early reports have been substantially mis-translated.

This answer make it clear that you'd have to dramatically reduce the salt content of sea water to get any kind of hydration benefit.

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    Note that the polynesians used to start drinking seawater before setting sail on multi-month-long voyages where they'd carry no water. As long as you don't de-hydrate before drinking seawater, it's quite sufficient to drink and survive on almost indefinitely. – Valorum Sep 25 at 19:07
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    @Valorum Do you have a citation on that? – paparazzo Sep 25 at 19:10
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    @paparazzo - Extensively discussed (and tried) in Alain Bombard's The Bombard Story. His legs swelled up and he suffered from early-onset renal failure but was able to drink seawater as his main source of water for weeks on end. – Valorum Sep 25 at 19:14
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    What exactly is your question? How to desalinate, or can one desalinate via cloth? – Martin F Sep 27 at 18:36
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    Vote to leave open - I am the author of the question and the answer at the proposed duplicate, This question and it's answers are not duplicates of it. – James Jenkins Sep 29 at 9:02
up vote 34 down vote accepted

Salt dissolves in water so will pass though a normal filter or cloth. You can try that with a coffee filter at home. So there's definitely an error in the article.

A still (i.e. distillation apparatus, whether solar or fire-heated) is the only easily improvised way to desalinate water, but the article I read said he caught and ate fish - that will provide some water, and if there was any rain to catch even some of the time that would be a huge help. He had some water with him at the start as well. Later reports have increased the estimate of how much water he had with him, and mentioned rain.

I suspect that, as has often happened before, the article said something like "survived by drinking seawater" when it should have said "survived despite drinking seawater".

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    "So there's definitely an error in the article." - Not necessarily; the error might well be with the guy's understanding of what you just explained. So I'm thinking he did do what the article mentioned ... with no effect. – KlaymenDK Sep 25 at 14:24
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    @KlaymenDK even if the author of the article (and I've now seen more than one) didn't make the error, they still repeated it. Maybe I've been spending too much time on science writing recently, but I don't have much patience for repeated errors, and certainly some reporters have reported it not as the individual's account, but as fact. – Chris H Sep 25 at 14:29
  • I've got a book on my shelf that among other stories contains a man who set out to prove it's possible to survive by drinking seawater. He has some remotely plausible claim that the body can remove excess salt by a slow process and went to sea to test it. – Joshua Sep 25 at 16:38
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    @Joshua: If you could summarize and provide a reference as an answer, that would be great. As it is, I don't know whether this was a fiction book, a posthumously published book, or a book showing that he was correct. (Actually, probably an answer to the question outdoors.stackexchange.com/questions/9920/…) – Seth Robertson Sep 25 at 18:25
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    I think, we need to wait to hear all the details about his water sources, if someone manages to make a good interview with him later on. The most plausible explanation is that he was drinking some rainwater. Fish contain about 50% water, so you would need to eat about 5 kg of fish each day to get 2.5 liters of water (estimated daily needs) out of them. You can't filter the salt out of seawater by usual clothing. And any amount of seawater you drink just worsens dehydration (outdoors.stackexchange.com/questions/9920/…). – Jan Sep 26 at 10:02

You can place an empty cup in the middle of a lightly filled bucket of sea water. You then place a plastic bag over the bucket, with a stone in the middle so it has a dip in it over the cup. The sea water evaporates, reforms on the plastic bag (without any salt in it) and then drips into the cup. Slow but far better than drinking sea water.

  • OK but this would be hard when you're on a boat and everything's moving around, and the question explicitly states "using clothing". – David Richerby Sep 25 at 16:44
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    @DavidRicherby, you can do that with clothing, e.g. a poncho. Besides, the Indonesian kid was drifting with some equipment (a wooden hut) that might have made it possible to apply this trick quite well, since he was apparently able to light a fire. – PatrickT Sep 25 at 17:29
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    This is called a "solar still". – Martin F Oct 1 at 19:29

Disclaimer: This is not safe. This is not well tested. This belongs here, not on the other question. This is weak evidence in collaboration for the drinking seawater claim.

On request by Seth Robertson:

Dr. Bombard made the attempt to sail across the Atlantic in a 15 foot boat called L'Hérétique to prove his claim that a castaway in the Atlantic could survive indefinitely at sea starting with no food or water. Particular quote:

"Now he had been at sea for 9 days and subsisting on up to 1½ pints of seawater with the liquid squeezed from the fish he caught each day. The seawater he said would satisfy thirst provided a person did not wait until dehydrated before starting to drink it. He must start drinking seawater from the moment he is cast away."

The doctor clearly thought he had an explanation for body chemistry as to how the body could extract and dump the excess salt from seawater, among all his dietary analysis that he did beforehand. Unfortunately this source doesn't copy it for us.

If I read the encounter right, there was no rain until 13 days in, but several points describe humidity in the air. He goes to great lengths to ensure there is no seawater on the topside to evaporate and leave solid salt.

Source: Chichester, Sir Frances, Along the Clipper Way, 1966 Chapter 3, pp. 19-34 SBN 345-02103-7-125 (SBN isn't a typo. That's what it says.)

There's some trouble with the attempt resulting in this being decidedly not a controlled experiment. On one hand, we would expect the fish he ate would be providing all the water he needed. On the other hand, he lost 50 pounds on the entire crossing. By the ordinary way of estimating if he's losing weight he's not getting enough water to live on in his food, raw fish or not. But 1½ pints of fresh water wouldn't make up the difference. He had rain starting on day 13 that provided plenty of fresh water from that point. This throws the weight number kinda off.

From time to time I hear another impossible sounding survival-at-sea story. For some reason a disproportionate number of these include the same idea of slowly drinking seawater. I can't imagine how it's really supposed to work. If the raw cooling is worth the salt, than bathing in it would work better.

I have cross-confirmed that Bombard's claim exists and a contemporary peer review resulted in a counterclaim. I can't read it though.

Somebody else's summary provides a rather implausible explanation for how the salt extraction works:

"What does for many castaways is that once adrift and with all fresh water exhausted, it’s only in a state of acute desperation that they turn to sea water (or urine). By now severely dehydrated, the kidneys can’t handle the sudden accumulation of toxins and an agonising death soon follows, supporting the mariner’s lore that drinking seawater was fatal."

https://apaddleinmypack.wordpress.com/2011/06/29/lindemann-and-bombard/

Except we know that's wrong. The kidneys can't extract salt into urine more concentrated than the blood. But Dr. Bombard couldn't have known that. It's barely possible that there's something else going on here that really permits this to work, quite possibly only for certain people. But if so, nobody's got a clue.

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    We have no real data about his actual water sources...The idea about drinking seawater "slowly" comes from an illusion that the saliva in mouth will dilute the salinity of seawater. This is ridicilous. The kidneys need to excrete any excessive salt you have ingested regardless of how slowly you consume it. In order to excrete the excessive salt from 1 liter of seawater you drink, the kidneys need to excrete 1.5 liters of water from your body, which results in 0.5 liter of net water loss (medicalsciences.stackexchange.com/questions/9275/…) – Jan Sep 26 at 10:41
  • @Jan: I am absolutely confident that Dr Bombard made no such silly mistake. – Joshua Sep 26 at 15:52
  • it seems that no one, except him, knew what were his water sources. Howmuch stored water he had with him? How much fish he ate? How much rainwater he drank? The fact is you cannot normally survive by drinking only seawater. Any amount of seawater is harmful. It's not that small amounts or slow drinking can help. – Jan Sep 26 at 16:23
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    I do not know if he lied or not. The thing is that nobody seems to have a reliable list of water sources he used. On Wikipedia it is mentioned he encountered a ship and the crew offered him a meal. But what was that meal - did it include water and did they give him more water for later? You can't make any conclusions from one's man story. You can believe it if you want, though. – Jan Sep 26 at 16:34
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    So, one thing that comes to mind is that cats have kidneys efficient enough to rehydrate themselves with seawater. So biologically it would be possible for someone possessed of higher-than-average efficiency kidneys to survive on seawater. A slow increase in salt intake might also trigger the kidneys to use a more efficient mode of operation. I have never been able to find record of any studies designed to look for either effect, but people who survive longer than they should have drinking seawater may count as some slight evidence that one or the other might obtain. – Perkins Sep 26 at 23:10

There is a summary of the Bombard voyage in Surviving the Extremes by Kenneth Kamler, MD, who started his explorations into extreme environments through climbing. On one of his Everest trips in 1996 he treated Makalau Gau and Beck Weathers for severe frostbite. Kamler says:

....Alan Bombard, a voluntary castaway...in 1951 crossed the Atlantic in a rubber raft without supplies of food or water. He set out from the Canary Islands and drank nothing but seawater during his first seven days adrift. Once he began catching fish, he ate and drank them, alternating the fluid he extracted with small amounts of seawater. He landed in Barbados sixty-five days later....

Earlier, Kamler said:

A person with no water intake at all will lose consciousness in three to four days and die in seven to ten days. A person who drinks seawater will also die within seven to ten days but will remain conscious almost to the end. This is because the body naturally loses a little salt every day. If you limit the amount of seawater drunk to a pint a day, salt buildup will be slow, and body cells will absorb water. After about a week, however, the salt accumulation will overwhelm the kidneys, and they will shut down.

Kamler discusses Thor Heyerdahl's Ra II expedition, which because of a mishap, had to jettison much of its fresh water. They were sailing in an area of the ocean whose salt concentration was less than 3 percent, so they added one liter of sea water to two liters of freshwater and survived, with some hallucinations.

Kamler also discusses how to wring water out of fish fillets and turtle meat using a shirt. He mentions Lynn Robertson, a nurse adrift with five other people, who gave rehydration enemas to herself and her family from the first, undrinkable collection of rainwater on their collection tarp, which was salty and containted bits of disintegrated rubber from the tarp. Rectums have membranes that extract water This is how seabirds extract fresh water from seawater. Another source of food and water is from the seabirds that alight on the raft as a resting place, and from the life that collects under the raft, from barnacles to crustaceans to fish. These attract larger fish, which follow along.

Within a week or two, a marine ecosystem will develop -- a food chain linked linked to the boat, literally within reach.

  • This is a great collection of information, and I see you've even found a specific reference to the use of clothing. – uhoh Sep 29 at 6:58
  • Do you know if "membranes that extract water" means that it leaves the salt behind? Or is it absorbing it just as it would have if it we drank it, such that it's still salt-water? – Aaron Oct 1 at 17:53
  • And I have other questions now too, such as: Why was the rainwater salty, or was it just mixing with salt already present on the tarp? Perhaps I should read that book. – Aaron Oct 1 at 17:54
  • @Aaron The collected water was salty because ocean spray and waves hit the tarp, evaporated, and left salt behind. As for the rectum, I wonder about that too. From the context, it means that the rectum does not transmit the salt to the organs, but how the rectum maintains an acceptable level of salt on its "exterior', I do not know. I guess that excess salt beyond a certain point is washed out by seawater, so the "exterior" of the rectum is salty, but not too salty for the organism. – ab2 Oct 1 at 21:33

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