Isn’t pee too salty to be a good option for drinking? If not then every person ever who was dieing from dehydration could go a lot longer if they drank their own pee. But that never happens. Either because no one ever wants to drink their own pee or it doesn’t work. I’m guessing it is the latter more often than not.
If you’re very dehydrated you won’t be peeing much.
That doesn’t surprise me. Last year, in a rather dark, but somehow functional, period mentally, I probably went one week, maybe two, where I consumed all my calories via beer or wine and that was my sole source of hydration. I did not experience any thirst issues, dark urine, or anything like that suggesting dehydration. I did not keep an intake diary, of course, so this is based on my recollection, which may be incorrect due to the alcohol, but my intake wasn’t enough to get drunk, but just enough to feel “normal” in a high-stress period.
I remember after a night of beer drinking in a park by my friends back in my teens (I was present, but not a beer drinker), one guy had refilled every one of his empty bottles with pee (for science?). It was a wash.
The water that is lost from drinking seawater is not in the gut, but due to filtration in the kidneys.
The large intestine uses active transport to move sodium against it’s gradient, and the water goes with it. The problem that arises is that sodium, unlike alcohol or sugars of various sorts, cannot be metabolized further into water and carbon dioxide.
That’s where the problem comes in with filtration in the kidneys. The system is more complex than the absorption of sodium and water in the colon, and involves multiple organ systems, hormones, and various feedback mechanisms. The main problem, however, is that human kidneys can’t concentrate urine enough to maintain water balance by the consumption of seawater.
https://www.jci.org/articles/view/94004
Something like sugar or alcohol would have the same effect if they remained in that form, and in fact this does happen in uncontrolled diabetes when the kidneys have to start excreting glucose in the urine, along with water to dilute it. Fortunately, under normal circumstances, we can metabolize alcohol and sugar by other means before they build up to the point that the kidneys have to excrete them in amounts that lead to a negative water balance. Sodium ions, unfortunately for anyone who tries to hydrate with ocean water, can’t be metabolized under the type of circumstances suitable for human life. There isn’t anything our bodies can do with them other than elimination in the urine, and sweat to a lesser extent.
ETA: There is a situation where sodium and water loss from the gut does present problems. Cholera toxin will inhibit the active absorption of sodium in the gut (among other things - chloride ions play a larger role than sodium) and in this case, the situation you describe does occur. Water moves down it’s concentration gradient into the gut, causing diarrhea, with disastrous results back in the day before IV fluids.
It is, and at a certain point you lose more than you gain, pretty much all hard liquor is bad, beer is fine, and most wines are OK.
We had a long thread about this, maybe a year ago?
Coffee is Ok, maybe pure espresso might not?
I would say beer is better. It has food content.
I’m not really sure what it would mean to “metabolize” sodium, but your description of what happens in the intestine is too simplistic, and the outcome is not what you describe. I’m very rusty on this stuff and my knowledge of physiology was never great but I’ll do my best…
Consider what happens in digestion of food. As food is digested, it forms a solution in the intestine with very high osmolarity (far higher than seawater). The osmotic pressure initially pulls water into the lumen of the intestine in the manner you describe. However, the nutrients (including salt) are then absorbed across the intestinal wall by active transport. This lowers the osmolarity in the lumen, until eventually most of the water is reasbsorbed.
Secretion in the Small Intestine
Physiology of Intestinal Absorption and Secretion - PMC
Similarly, if you drink a salt solution, the salt is actively transported across the intestinal wall, lowering the osmotic pressure in the lumen until the water is absorbed also. It doesn’t matter (up to a point) if the salt is more than you need - the body does not manage sodium homeostasis by secreting water into the lumen of the intestine.
Excess sodium is managed by renal excretion, and the problem is that the kidney can only concentrate sodium to about 2%, vs the ~3.5% concentration of seawater. Hence the requirement for more water than you initially drank to dump the excess salt in urine.
I won’t claim to understand exactly why the kidney has this 2% concentration limit, it’s a complex process…
I just saw @FlikTheBlue comprehensively ninjaed me while I was writing all that…
That was what I was getting at. Sodium ions are inert in the type of environment that the human body consists of. The only option to maintain balance is to excrete them.
I think this ultimately comes down to the fact that it takes more energy to maintain larger concentration gradients. Since humans and our ancestors didn’t evolve in the type of environment in which we would benefit from the ability to drink seawater, there wasn’t any evolutionary pressure to select for a mutation which would otherwise be disadvantageous due to those having the mutation having higher caloric needs than those without it (to maintain that higher concentration gradient).
Yes, I had not seen your post while I was writing mine. I needn’t have bothered!
Which begs the question of what sea-dwelling mammals can do. According to this seals and sealions can concentrate urine much more than humans:
Apparently we haven’t studied other animals. Nobody wants to do their PhD collecting urine?
If you are lost at sea in a canoe with a sexually compatible companion, is it true you can create light beer, which you can then drink to prevent yourselves dying of thirst?
No, because despite popular opinion, it’s not fucking close to water.
What I read in a survival manual was, you are supposed to sip (a certain quantity of) seawater, not because you will survive any longer, but because it will extend your time of useful consciousness by a day or so.
If you have a limited supply of fresh water, you can also mix it with seawater, to make something that’s fresh enough that you can still process it, and thus stretch your supply a little.
Though I don’t know what the optimum ratio is.
And thanks to @FlikTheBlue and @Riemann for the corrections.
Assuming the 3.5 % figure Riemann cites for seawater is accurate (let’s round up to 3.6 to make the numbers neat), then a 3 to 1 freshwater to saltwater mix should do the trick. The idea would be to get a solution that’s 0.9% saline, which is the level our plasma is at. Drinking the fresh water by itself would lead so some inefficiency compared to drinking a 3 to 1 mix. Mixing it like that would be the equivalent of having 1 liter of Gatorade (minus the sugars and flavorings 
) vs. 750 ml of pure water.
Years ago, I read a first aid booklet that talked about inducing vomiting when someone had ingested certain poisons. One suggested emetic was saltwater.
Is seawater not saline enough to cause vomiting?
The survival manual I read said 10-1.
Maybe they were being conservative.
Probably not.
Weren’t beer and wine pretty much the only things people drank in the middle ages, when potable water was hard to come by? There’s even a theory that beer was essential to civilization; there was a documentary about it. ‘How Beer Saved the World’ brings light to age-old debate | Entertainment | the-standard.org
That’s why I said “up to a point” in saying that both the salt and the water in seawater would initially be absorbed by the intestine. If you chugged down a lot of seawater on an empty stomach, you might just vomit. But a deliberate emetic would usually be a much higher concentration. And it can be dangerous.
https://pmj.bmj.com/content/postgradmedj/50/586/513.full.pdf
This link describes a fatal outcome from use of a salt emetic after a mild overdose. The salt concentration for the emetic is given as 2600 mEq, which I think works out to about 15% (seawater is about 3.5%).