Ways to desalinate water when "lost at sea"?

Question

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

• Jakarta Post Indonesian teenager survives 49 days adrift in Guam waters
• NPR: 19-Year-Old Survives 49 Days At Sea After Floating Hut Drifts To Guam
• The Guardian Indonesian teenager survives 49 days adrift at sea in fishing hut

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.

Answer 1

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".

Answer 2

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.

Answer 3

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.

Answer 4

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.