If a person found themselves adrift at sea with a very limited supply of fresh water should they add sea water to the fresh water to increase their overall supply of H2O?
For the purposes of this thread, assume the hypothetical person also has a very limited variety of food and none of it supplies the sodium and potassium s/he requires (note: I am unsure about the amount of potassium in oceans, so take that part with a grain of salt).
Should the person add sea water to the fresh (or otherwise consume it)? If so, how much? What should the dilution be?
If not, why not? I understand the general reasons why you can’t survive (and would even hasten death perhaps) by drinking only sea water, but it seems that if the salinity were lowered enough the water would hydrate a person *and *give one the necessary sodium/potassium etc.
According to the Google of recommended drinking water standards there should be no more than 20mg/liter of salt in drinking water. This is no doubt the standard from continuous use. If you are only going to be doing it for a while maybe you could double this.
So it appears to me you would have to dilute the salt concentration in seawater by a factor of 3500/4.
We have medical people here who can adjust the tolerable amount of salt depending upon the length of time you will be on such a regime, assuming the time matters.
I’ve read somewhere (no cite unfortunately), that drinking a small amount of seawater per day is actually beneficial, as the kidneys has the ability to process the salt. I think (based on a faulty memory) that the amount was something like 200-300 ml per day. If so, diluting with a 50% mix of fresh water, simple logic would seem to dictate that you could then drink 400-600 ml of this mix without ill effects.
It was based on an article written by Alain Bombard, but according to the Wiki entry it has since been disproven. As for why one would want to, it was in response to the OPs premise of stuck at sea with little fresh water.
According to Wikipedia any intake of saline water is negative, as it will cause you to dehydrate more than you consume waterwise, regardless off amount. So please disregard my previous post.
Untrue. Virtually all fresh water does contain some sodium. Water softening treatments frequently use salt. Only distilled water would reliably be without salt.
When rehydrating people medically saline is used - saline adjusted to match the normal salinity of the human body. You do need some salt, just a very small amount.
The key is that the salt is kept below a certain level, the maximum level your kidneys can manage. I read a book on survival once that actually described an experiment done such as proposed in the OP, utilizing a mix of fresh and seawater, but the mixture was monitored by use of salinity measuring tools that are unlikely to be in a standard marine survival kit and require some skill to use.
Meh I cant seem to get my posts correct What I meant was salt water as in ocean water - with that amount of salt in the water, it will cause you to lose more water than you gain even if sipping small amounts (according to the Wiki as I understood it.)
I have read a number of stories about men during WWII that were adrift after their ship was sunk.
Drinking sea water caused them to go crazy and die The ones that survived were the ones that resisted the temptation to drink some of that water no matter how thirsty they got.
So based on that, I would say that it was a bad thing.
I read a story of a French guy (I think) who set himself asail across the Atlantic in a raft to prove that it was possible to survive on seawater and fish caught on his voyage. He did survive, but he was extremely careful when sticking to his regime and only drank minute amounts each day.
Does anyone remember his name?
EDIT: he’s already been mentioned. Alain Bombard’s story sounds like the one I remember.
I was not asking about *only *consuming pure sea water–I think that’s well-known to be bad news. My question in the OP was about adding sea water to fresh water to extend your supply of water (and provide you with needed sodium) so as to hopefully live longer.
I’m curious if this is officially recommended anywhere as a survival strategy (if lost as sea). Is there any reason why mixing sea water into your fresh water supply at the proper dilution (and what is the perfect dilution anyway?) would not help you survive longer than drinking fresh water alone? (given a limited fresh water supply, of course)
We had a thread on this a while back, but search is wonky.
Basically, NO!
Your body will buffer things just fine. The kidneys will use the fresh water appropriately. One needs about 500 mg of NaCl a day, and that’s about a quarter of a teaspoon. You’ll get that in your emergency rations or, failing that, just by breathing the sea air!
So don’t add to your osmotic burden by adding salt water to your water. Your body will just pull fresh water from your cells to dilute it.
I think you’ve missed the point. If the salt water is diluted to below the concentration level of the kidneys then the body won’t need to pull fresh water from your cells to dilute it. The kidneys will demand more energy to reclaim the water from the filtrate, but no additional water will be lost so long as the salinity of the water is kept below what the kidneys are capable of producing.
The idea here would probably be to dilute the salt water down to level comparable to Gatorade which of course does not "pull fresh water from your cells " despite being essentially dilute saline.
This post in this thread gives you the amount of salt in a liter of seawater. The number is 35 grams/liter.
Qadgop has given the amount of salt required per day. If your drinking water is distilled water and your emergency rations give you 480 mg then you can take in an additional 20 mg assuming no other salt intake (don’t let the sweat of your brow run down into your mouth). In that case a liter of seawater would have to be used over a period of 1750 days or 4 years, 9 mo. and 16 days.
So it’s just a wild ass guess but I would say that no survival guide would recommend mixing sea water with your fresh water to extend your supply. Better to be a little short on salt rather than long I would think since excess salt dehydrates you.
The problem is that you are conflating “minimum dialy requirement” with “minimum acutely toxic quantity”. The two are in no way related and you can’t simply interchange the two as you have done.
While your body only requires 500mg of salt daily it can tolerate far, far higher quantities. Hell, we’ve probably all absorbed over 10 times that dose of salt in a single day just by eating badly.
The information we really require is at what level salt actually becomes acutely toxic. IOW how much can we tolerate before it will kill us faster than normal dehydration. So long as we keep below that level then we can stretch our water supply by diluting down to that level. Yes it will put additional demands on the kidneys. Yes it will require more food. Yes it will kill us if we do it for years, but so long as it doesn’t kill us faster than dehydration then we come out ahead.
If forced to the kidneys are capable of producing urine that is about 2% salt. That means in effect that so long as we dilute our sea water down to 2% or less the kidneys can remove the water and get rid of the salt for us. In contrast sea water is about 3% salt. That means that if we drink 1 litre of pure sea water we will lose more water than we gain, about 300mL more. If we drink 1 litre of fresh water then we gain 1 litre of water. But if we mix 1:1 sea and fresh water than we produce a solution that is 1.5% salt, well below what the kidneys can produce. We have thus gained 2 litres of water from the use of one litre of fresh water.
Note that the above ‘calculations’ are very much back-of-the-envelope, and make all sorts of unsupportable assumptions, but hopefully you see the point. There is some dilution of sea water that will produce a net gain in physiologically available water because the kidneys themsleves are capable of deslinating mildly saline water. I’m not entirely sure I would ask my kidneys to produce 2% urine for very long, but certainly 1.5% should be sustainable for longer than the few days that it can take to die of thirst.
The question to be answered is how much the water volume can be increased by adding salt water before the benefits of the volume increase outweigh the liabilities of the salt water.
My gut feeling is “small to none”, recalling what I do about intra vs extra-cellular fluids, 3rd spacing, and how nephrons function.
And it’s more complex than just figuring out the sodium levels, because seawater will contain potassium, iodine, chloride, and bromide, among other trace ions that the body will have to deal with.
I did look for an algorithm which would address this point just from the standpoint of NaCl content, but was unable to find one.
That makes no sense to me. If we follow the logic that any mixing of salt with fresh water has a negative effect on water balance then there is no natural source of potable water on the planet Earth. All natural water conatins some salt, yet people manage to regulate their fluid levels perfectly well by dirnking it.
Quite obviously there is some level at which drinking dilute saline has a positive effect on water balance. The question is simply one of what level that dilution has to be.
It seems like the article quoted has decided to play it ultra-safe and simply declare that even diluting sea water to 1ppm with fresh will not increase the total amount of physiologically available water.
Great post. This is exactly the sort of stuff I am after. I hope to find out whether people should be trained to mix sea water and fresh water to survive longer if stranded at sea, and if it is a good idea, why isn’t it taught or utilized as a survival strategy? (or is it?) In addition, shouldn’t the food rations in a lifeboat (or what have you) on an ocean going vessel contain absolutely NO sodium so that more sea water could be mixed with fresh water yet have you remain within you daily acceptable saline toxicity levels?
That was an interesting document. I must say, I didn’t understand the *“absolute prohibition … needed against drinking seawater or mixing it with freshwater.” * Or the part about the *“shift from intracellular to extracellular water.” * It just seems common sense— even taking into account the other stuff present (potassium, etc)-- that if properly diluted, the sea water could be constructively utilized.
My non medically-trained brain would need to have it explained in fuller detail, I guess, but it seems that on the face of it, the cite from Qadgop explicitly says not to mix the sea and fresh water.
On review after seeing Blake’s newest post: Yes. That is exactly the part I would need explained to me in greater detail. Why can’t you mix sea water and fresh water and safely drink it if it is, let’s say, 1,000,000 parts fresh water to 1 part sea water? Surely some dilution is safe, so what’s with the “absolute prohibition”?
Paging KarlGauss. He’s an academic internist who knows acid-base stuff and renal physiology better than I. Also a shout out to Chief Pedant, Doctor J, other knowledgeable docs on board, and any renal specialists we have in the vicinity.
I still don’t think you’ll be able to add significant volumes of seawater to your freshwater supply before you cause further harm, but can’t articulate just what that amount should be. And my Google Scholar skills are failing me.
What I meant was salt water as in ocean water - with that amount of salt in the water, it will cause you to lose more water than you gain even if sipping small amounts (according to the Wiki as I understood it.)