So now we come to the situation of the poor soul who has diligently read today’s item and a year from now finds himself out in the atlantic in a zodiac, recalling your important instruction. If he (or she) is a Thinking Person, i’ll bet the next thing he thinks is “Well, OK, as awful as it sounds, i must now consider drinking my own urine in an attempt to stay alive.”
OK, NOW what does he do? How will THAT affect his bodily condition, good or bad? you didn’t address that!
As he dehydrates, his kidneys will kick into a higher gear until they reach the point where they can no longer remove salt and waste from the blood.
Seawater is already way past that point.
He will live the longest if he drinks his urine from the beginning, when it is least salty. If he drinks it beyond the point of equilibrium, it will do no good, but probably no harm.
I have some knowlege of basic physiology, but this is purely speculation.
Welcome to the Straight Dope Message Boards, gallant205, glad to have you with us.
When you start a thread, it’s helpful to others if you provide a link to the Staff Report upon which you are commenting. Helps keep us all on the same page. Especially when, as in this case, the Staff Report won’t actually “appear” to most members until Tuesday coming.
I’ve taken the liberty of editing such a link into your post. No biggie, you’ll know for next time.
And I confess, I have no idea about how long drinking your own urine will sustain you, but I suspect not that long – after all, the urine is full of the junk your body is trying to get rid of. However, that’s just a wild-arsed guess, I didn’t look into that aspect.
hey, thanks for fixing my post. i’m not upset, i’m happy. i have NO idea how to do that with something from the webpage or from an email, such as i received.
“Drinking even a little seawater starts you down a dangerous road: The more you drink, the thirstier you get.”
In my experience, you can get that effect from a lot of other drinks besides seawater …
(1) Click on FAQ in upper right corner of this screen
(2) Scroll down to “Posting Messages” and to the question on “special codes” and click on that
(3) That will lead to "For more information on vb codes, click here
… and that’ll explain it
OR:
Just type the URL, and the boards will make it into a link
OR:
Type {url} at the beginning and {/url} at the end, using square brackets [ and ] instead of curly brackets.
So, if you find yourself drifting on the ocean in a rubber life raft, is it feasible to make some kind of evaporative desalinator to supply yourself with fresh water?
Yep. All you need is some kind of plastic sheet and a container like a can or jar. Suspend the sheet from the edges of the raft and put a weight in the centre, and the container under that spot.
Now cover the bottom of the raft with a thin layer of seawater (or urine). The water will evaporate, condense on the sheet, run down to the centre and drip into the container.
You’d be best to scrape out the depositing salts etc every now and then, but that’s about it.
So, what variables would affect the … uh … feasibility, I guess, of this? By which I mean, whether or not it would provide enough water to sustain your life. The size of the sheet, I would assume … and how hot you can get the liquid under the sheet, as the hotter it gets the faster it evaporates … and … uh … that’s all I can think of.
So is there a way to calculate how big of a plastic sheet you would need to provide enough water for a given air temperature? Obviously this method of desalination is going to produce more water if you’re drifting in the South Pacific under the harsh glare of the tropical sun than it will if you’re huddled up on a frigid raft in the middle of the Arctic Ocean. But is it still possible to get enough drinking water to live on even if you’re not in the hot sun, assuming that the temperature is above the freezing point of water?
(Apologies if my post is not quite intelligible. It’s been a sleepless night again, and I’m pretty much running on autopilot.)
I’m not so sure. For good condensation you need the sheet to be cooler than the air. But maybe in the tropics the increased humidity compensates for the higher temperature of the sheet. And note if you’re in the Arctic you can probably get floating ice to melt and drink, your limit here is hypothermia.
More study is needed. Let me know when you’re done.
So, next time someone asks you the old chestnut about being stranded on a deserted island with only three books and what books would you take, the best answer is: a filled water cooler, a bottle of scotch, and another filled water cooler.
Nathaniel Philbrick’s popular recent book In the Heart of the Sea: The Tragedy of the Whaleship Essex includes a number of interesting, if grisly, accounts of dehydration. Not all of the sufferers were at sea, but their symptoms were similar. What I got out of it is that it is no fun to be thirsty in the desert, but at least you are not likely to be tempted to drink something you shouldn’t.
Actually, that brings to mind another question: what is the salt content of sea ice?
I think that the ice crystals themselves will be pure water. But won’t some amount of salt be trapped in the bulk material? Will this be enough salt to cause problems?
First of all it is kind of weird to say salt is metabolized since it goes in NaCl and comes out NaCl, but ignoring that, I have an important question. Salt water is bad because it is roughly iso/hypertonic to blood so it saps our water to get rid of it. What if instead of drinking sea water you sat outside the boat and soaked in it. Your body, if sufficiently permeable to water and impermeable to its own solutes (if it weren’t all your proteins would diffuse into the ocean) would maintain isotonicity with water and you would stay alive. So I ask, if you soaked in the sea would you do alright?
Well, that would still leave you thirsty. Your outer skin cells might (I say might; I’m not sure) be sufficiently hydrated, but taking a bath wouldn’t do diddly for your innards.
I’ve heard that at one point in the Atlantic crossing, Magellan’s sailors were desparate enough (and irrational enough) to try drinking seawater, and found to their surprise that it was fresh. It seems that the Amazon current is so strong that it carries fresh water out beyond sight of land, before mixing with the salty ocean water. Anyone know if there’s truth to this?
I’ve heard the same, and wouldn’t be surprised if it were true that there is fresh water well out to sea there (as the Amazon has the biggest flow of any river). No idea on the Magellan bit though. Did he actually go anywhere near the mouth of the Amazon?
I recall reading an article - reprinted from the original source into Uncle John’s Bathroom Reader (guess what I was doing at the time) - that mentioned a European man that insisted that drinking salt water was fine, as long as one didn’t wait until one was already dehydrated before one started drinking. To prove his point, he set out across the Atlantic, alone, in a raft, and drank just salt water the whole time. He survived the trip, after several weeks, without too many health problems.
No, the story is myth, for the reasons outlined in the article this “trick” is a road to just as certain a death.
However I would like someone with more background to work on the question of soaking in the sea to get water. What is the osmostic gradient there. I know Chronos, you have your doubts, but anything that can get into a venous (blood or interstitial)system is all the body needs for hydration. Water need not penetrate much more deeply than the skin to be useful since even at that layer there is a huge circulatory network. The depth that water can quickly travel is an easy experiment to conduct on yourself. Simply sit in the tub for an hour and watch water travel up its osmostic gradient into your skin, leaving you pruney. The pruning is due to the uneven hydrostatic swelling of your skin. If the osmotic gradient of saltwater is roughly equal to that of the body, you should be able to soak some up. Since the skin has essentially no permeability to charged particles such as salt the water will go into the body and the salt will stay out. I’m sure many of you have seen this effect in high school with a dialysis bag. Anyways at the very least the oceans pressure should greatly discourage evaporation. Can we get a physiologist, chemist or the great Cecil to ring in on soaking in the sea.
