If you are stranded at sea with no water, is there a point where drinking salt water will benifit you more than it harms you?
General rule I assume is no, but I have heard if u have any way of getting fresh water that you can mix it (1:1?) with salt water and its safe to drink, kinda like a survival gatorade. I think I saw that on a survival show, surviverman or man vs wild.
No. Seawater has more salt than your kidneys can get rid of through urination. You would end up dying from dehydration.
You can drink it, but you’ll die if you don’t get fresh water before long.
So even if you are compelty dehydrated and on the edge of death, even drinking a few sips of sea water will not help you?
If you’re completely dehydrated and on the edge of death, a few sips of fresh water won’t help you either. You need at least half a gallon of water to rehydrate, and roughly a full gallon per day, double or triple that in hot and dry outdoor survival situations. Survivorman did say once that you can drink about a mouthful of seawater a day, which can help replenish your electrolytes and some other minerals, but only if you’re also getting fresh water. It’s pretty vile too.
It’ll make you feel a little better in the short term. But in the long term, you’ll end up either more dehydrated or dead.
Seawater is also dangerous because it’s full of bacteria and viruses. Granted, most of them are evolved to infect sealife. But there’s no guarantee one of them won’t make you sick.
You could drink the water from the Baltic Sea since it’s a lot less salty, getting close to normal fresh water the closer you get to the northern end of the Gulf of Bothnia. There’s no nice uninhibited little sandy islands with palm trees there to be stranded on though.
If you get them drunk you could talk them into some fun.
Dammit, spellchecker only tells me when it’s not a word, not when it’s not the right word. 
“Ah, water. Never touch the stuff. Fish fuck in it.” - W.C. Fields
Seawater may have toxins in it that are dangerous. Fresh water is more likely to infect you with micro-organisms than seawater, but coastal seawater is often polluted, and that pollution includes diseases from sewage that can be very bad for you.
There is a fair bit of evidence, although it is little-known, showing that the worst effects of drinking sea water are not from the water itself, but because virtually everybody who has drank it has waited until they were severely dehydrated first.
It’s still not a good idea, and you don’t want to do it for long, but being hydrated helps considerably.
http://www.naturalhistorymag.com/picks-from-the-past/181950/thirst
But even if you accepts these anecdotes as weak but valid evidence, they are uncontrolled, and they certainly do not show that drinking the seawater was beneficial. In both cases, unlimited fresh water became available after a few days, so they may have survived despite harmful effects from the seawater.
No. That would be even worse than doing without. Your blood must be slightly less salty than sea water. Your pee must be even less salty. If you drink any sea water, at any time, you must drink some fresh water soon after, in order for your kidneys to have the water they need to get rid of excess salt. You can try that right at home* – make a tall glass of salty water, and drink it. You will be thirsty enough, soon enough, to let you know, just because it was fluid, doesn’t mean it was drinkable.
*Please don’t experiment with your own body if you have serious kidney, hypertension, or other ailments. Please don’t drink just Gatorade on a hot summers day, while performing heavy outdoor work, if you have poor health, etc.
Certain marine animals have a trick, they excrete extra salty tears, so salty it almost comes out solid. They can drink sea water.
I have read survival guides that do suggest, once you have rehydrated, that there is a safe mixture of sea and fresh water, something like 3/4’s fresh to 1/4th sea water that you can use to stretch your supplies. You can double check that, when you next expect to be lost from civilization.
To my mind, absent other information, the questioned was answered by cochrane above. Human blood is around 150mM; seawater is around 600mM; the maximum concentration that the kidneys can achieve in urine is around 300mM.
http://jap.physiology.org/content/14/6/1036
So, drinking seawater will dehydrate you, because the kidneys will need to use up additional water to make enough urine to excrete the excess salt.
Given this, I think the burden is upon those who advocate even diluting seawater with fresh water to show that it’s more beneficial than just drinking just the available fresh water (beyond, perhaps, a very small amount of seawater to replenish salt lost in sweat).
How about the old tale of bilge water in enema form being adequate?
Bilge water is likely to be seawater, but let’s specify that we are using water straight from the ocean, no bilges involved.
Could seawater be absorbed by the colon with no lasting harm, even if any crud left in the colon stays there for months?
Transport of water across the colon membrane occurs by osmosis. The high salt concentration in seawater would mean that the osmotic pressure is in the wrong direction. So water would pass from the body into the colon if the colon were filled with seawater. I don’t think this would end well.
Of course the Nazis also did human-seawater-drinking experiments. Horrific (and fatal) as you’d expect.
I’d guess that in a survival situation even splashing seawater onto your face would be a bad idea. The salt is going to wick away even more moisture from your skin.