Why Can't We Drink Sea Water?

http://globetrooper.com/notes/why-cant-we-drink-sea-salt-water/

by todsul • 15 years ago

217 83 15 years ago

dpcan• 15 years ago

This is an article about why we can't drink salt water :)

On hn I usually expect these titles to be tongue in cheek and the article to be about an invention that would allow us to inexpensively purify sea water for drinking.

Speaking of which, IS there such a device? If not, why not?

zandorg• 15 years ago

In the film Waterworld, they have a device to purify urine - you crank the handle - but funnily enough they aren't using the device to clean seawater. Just another plot hole...

iqster2• 15 years ago

They have desalination plants in the middle east. The problem with those is that they are very energy intensive.

Roboprog• 15 years ago

The suits in the novel "Dune" do that as well. But there is no ocean or other open bodies of water on the planet in the story.

Radim• 15 years ago

Evaporation would leave the salt (and most other minerals) behind.

I suppose there exist devices for re-capturing the condensed (=drinking) water out of sea water. I don't know why they're not common; my guess is they're just not economical/too hard on maintenance.

FreeFull• 15 years ago

The point is that you condense the evaporated water. You can do this more than once to get purer water. One thing though, you'll end up with a significantly smaller amount of water than you started with, so you have to compensate for that.

bch2• 15 years ago

> Evaporation would leave the salt (and most other minerals)

That's a good point. I can't say I know the answer, but I've read/heard that drinking this mineral-free water can have long-term adverse health effects (leaches minerals from your body into the mineral free water?). I see articles for/against this theory. Interested to hear comments from anybody who actually knows details.

Of course dying from thirst or salt poisoning in a few days versus the long-term prospect of slow mineral loss make the choice a no-brainer in the case of an emergency.

latch2• 15 years ago

Not really, and for the same reasons the combustion engine is still king: so far, there's almost always more economical alternatives. The biggest issue is the cost of energy.

toyg• 15 years ago

Such things do exist, but they are so energy-intensive (water has to evaporate) that they're only used in extreme emergencies. Plus, doing it on a large scale would have effects on things we don't fully understand yet (sea levels etc).

jacques_chester3• 15 years ago

> (sea levels etc).

Well, no, because the water that comes out of the sea, one way or the other, will probably go back there.

The main problem with desalination is what to do with all the salt it produces. I mean, you can dump it at sea, but then you're poisoning some patch of sea and hoping the salt will disperse.

mseebach2• 15 years ago

> (water has to evaporate)

The most common method of desalination is reverse osmosis. Still energy intensive, but presumably less so than evaporation.

http://en.wikipedia.org/wiki/Reverse_osmosis#Desalination

todsul2• 15 years ago

Define inexpensive.

A lady has just put up a group trip to row across the Caribbean Sea. 14 people will row a double-hull boat over more than a month. They'll definitely need to desalinate sea water.

http://globetrooper.com/caribbean-sea-row-2012-barbados-jama...

Katadyn does desalinators for civilians.

http://www.katadyn.com/usen/katadyn-products/products/katady...

carsonbaker2• 15 years ago

For those interested in watermakers, it's possible (and perhaps affordable) to build your own!

http://www.albin25.eu/our-a25ak-dido/34-dido-stories/60-dido...

acangiano2• 15 years ago

http://www.thewatercone.com/Index.html

ChuckMcM• 15 years ago

That is so cool. We built solar stills in scouts but this one seems really practical.

kika• 15 years ago

And you can build such a thing on the sea beach with a plastic bag (which are a plenty on the beaches everywhere in the world, imho).

jerrya• 15 years ago

Based on a solar still, http://en.wikipedia.org/wiki/Solar_still, there is the Water Pyramid for villages, http://en.wikipedia.org/wiki/Water_Pyramid and the Water Cone for personal use: http://www.thewatercone.com/Index.html

Panoramix• 15 years ago

There's a Canadian startup making a device that gets (part of) its energy from the difference of ion concentrations in salt/desalinated water. http://saltworkstech.com/

hugh3• 15 years ago

Desalination plants? Sure, they're widely used in many dry parts of the world, particularly the Middle East, but also increasingly in Australia.

http://en.wikipedia.org/wiki/Desalination

According to International Desalination Association 2009, there are 14,451 desalination plants in operation worldwide, producing 59.9 million cubic meters per day (15.8 billion gallons a day), a year on year increase of 12.3%

iqster2• 15 years ago

I have to recommend a cool book on this ... Why Geese Don't Get Obese. It delves into the biological systems of different animals and explains how they do some amazing things. For instance, there was a chapter on how fresh water fish and salt water fish differ in how they drink water.

mechanical_fish• 15 years ago

Thanks, I was just wishing that this article would have gone into that.

Presumably whales and other marine mammals can drink ocean water -- how else would that work? -- so it's not an inevitable design constraint that our internal salinity is less than that of the ocean. Presumably our ancestors evolved to drink low-salinity water (and eat separate sources of salts, and automatically mix the correct salts into the water in the correct proportions, and maintain those proportions at all costs -- lots of overhead!) because fresh water is what's plentiful in our habitat. In other words, it's because lakes, rivers, and springs yield fresh water that we've evolved all these mechanisms for tolerating fresh water.

Another nice poetic question is: why are we made of so much water? The answer is that life evolved in the ocean. We're built out of crucial parts that were developed in the ocean and that can't operate outside of a saltwater environment. So life colonized the land by evolving a way to carry its own ocean with it. ;) I'm a giant EVA unit for ocean-dwelling cells!

jacques_chester3• 15 years ago

For example: house cats are believed to be descended from a desert cat. They have adaptations that make sense for a desert environment, such as dry poop, concentrated urine and very efficient kidneys. A house cat could survive on brackish to salty water for quite a while. You and I could not.

klbarry• 15 years ago

I'm surprised I was never taught this before. Great post.

carsonbaker2• 15 years ago

This is controversial, but Alain Bombard (http://www.nytimes.com/2005/07/24/obituaries/24bombard.html) sailed across the Atlantic, surviving on seawater, fluids from fish, and plankton.

Seems like you might be able to drink a little seawater, but not too much -- maybe a pint a day at the most. Natural History magazine has a great article on this:

http://naturalhistorymag.com/picks-from-the-past/181950/thir...

Loic• 15 years ago

A French biologist Alain Bombard as proved with a 65 day trip across the Atlantic that one can drink sea water up to one liter per day if one can drink raining water and water extracted from fishes too. So, yes, you can drink sea water, but not too much. So, do not keep in mind that you absolutely cannot, as it can bring you an extra day of survival (if you do not have other source of water).

http://en.wikipedia.org/wiki/Alain_Bombard

electromagnetic• 15 years ago

Actually if you're dying of dehydration, chances are you're somewhere exceptionally hot, because it's rare that you wouldn't be able to find water in 3/4 days in a temperate climate.

If you're in an area where you're perspiring a lot, then occasionally drinking sea water would actually be beneficial as there aren't many readily available sources of salt.

I work construction, in the longest heatwave of the summer I was putting tablespoons of salt into my water jug as it's quite easy to become nauseous when drinking a gallon of water inside a work day. Not to mention you don't want to get disorientated or light headed whilst 30ft in the air.

Long time survival in a hot environment requires a source of both fresh water and salt. The ocean is a far easier source of salt than searching for anything in nature.

mynameishere• 15 years ago

Wouldn't it be more pleasant to drink fresh water and take salt pills separately?

BerislavLopac• 15 years ago

Well the problem is just as the OP says: human cells have a low salinity. So pure sea water is bad, since it has a much higher salinity; but mixing it with fresh water (as that French guy mentioned by the parent apparently did) is ideal, as it brings the salinity level closer to the mark.

kia• 15 years ago

I down voted because you give a dangerous advice. The concentration of salt in sea water is higher than in urine. Drinking sea water rises the level of sodium in blood very quickly which sends signal to your kidneys to get rid of that salt. But as kidneys can't produce urine with the concentration of salt higher than certain level you need more body water to excrete the amount of salt you consumed with sea water. Roughly speaking you need 1.5 liters of fresh water to excrete the salt you got with 1 liter of sea water. Eventually the concentration of salt will become dangerously high in you blood and you will die of heart failure or seizure. So I would say that drinking sea water will actually DEPRIVE you of extra day of survival which may be lifesaving.

Modern survival guides consistently advice against drinking sea water.

Speaking of Alain Bombard. The most likely explanation here is that he consumed enough FRESH water (with fish and rain water) to dilute sea water he drank to safe levels for his body.

So if you are on a boat in the middle of the sea NEVER drink sea water. This can save your life.

philfreo• 15 years ago

> When we drink too much fresh water, excessive water passes into our cells to try to regulate the concentration (which can become futile)... If they absorb too much water, the cells will swell and burst, which can lead to a quick death

I've been scared of this since I was a kid, and nobody ever told me how much water was too much.

Cushman• 15 years ago

You'll get high from it before you'll die.

This is absolutely true. Too much water can induce euphoria, and can lead to dependence over and above what is necessary for survival. Water addiction is a serious illness; large psych hospitals have halls without access to water fountains for these people.

Google before you downvote, folks.

superted• 15 years ago

I drank something between 4-6 liters of water in a couple of hours time last summer, and ended up with fever and throwing up excessively for the remainder of the day. I was more or less knocked-out for the next couple of days. So I can definitely tell you that drinking too much fresh water in a short time frame is anything but healthy...

mseebach2• 15 years ago

Strictly speaking, you can't know if drinking the water did that. It could just as well have been food poisoning or heat stroke, or you might have been dehydrated prior to drinking that water.

acangiano2• 15 years ago

Your kidneys can only excrete 1L/hr under optimal conditions. So you were a victim of water intoxication, but were very lucky you didn't die. People died for drinking much less water than you did.

redler• 15 years ago

It sounds like you experienced water intoxication and/or hyponatremia.

http://en.wikipedia.org/wiki/Water_intoxication

http://en.wikipedia.org/wiki/Hyponatremia

mahyarm2• 15 years ago

It's a lot of water. Your body will make you feel like not drinking water anymore and sick long before you reach that point. You have to be basically be drugged or completely ignoring your body's signals. You'll also have to go to the washroom soon afterwards as your bladder fills up to deal with the excess water.

thret• 15 years ago

Water-drinking contests are a bad idea: http://www.msnbc.msn.com/id/16614865/ns/us_news-life/t/woman...

iwwr• 15 years ago

Kidneys like marine mammals have could help us.

Relevant: http://www.scientificamerican.com/article.cfm?id=how-can-sea...

russell• 15 years ago

Reverse osmosis is getting to be a viable water purification method even if you are not an energy rich middle eastern oil producer. Back in the 90s I lived in a community of about 160 homes in the mountains above Woodside CA. We had our own mutual water district. We had good water quality, but were pestered by the county to upgrade our treatment facility because our reservoir was subject to contamination. There was a gas station with leaking tanks about 50 feet from the edge. We finally installed a reverse osmosis filtration system, not to create fresh water from salty, but to remove any possible contaminants.

The town where I now live is planning to install a desalinization plant because the main water source was contaminated by MTBE contamination from the Chevron station. It is being held up by an over zealous coastal commission.

Retric• 15 years ago

Reverse osmosis takes more energy the more polluted the source is, because osmotic pressure increases based on the relative concentrations on either side of the semi permeable membrane. So don't confuse the costs of filtering contaminated fresh water with sea waster.

ordinary• 15 years ago

> There was a gas station with leaking tanks about 50 feet from the edge.

Why not fix the problem at its source (as well)?

zokier• 15 years ago

But why cells are so finicky about salinity? Why can't cells operate properly with some salt present?

jforman4• 15 years ago

Alas, this article is not remotely accurate. In truth, the best thing that you can drink when extremely dehydrated is lightly salted, sugared water (on an empty stomach, at least — food can provide the salt/sugar otherwise). This is why Pedialyte, which contains both salt and glucose, is often given to dehydrated children and adults. This is also why Gatorade is better than pure water.

The reason for this is that water absorption in your small intestines is significantly more complicated than depicted in the image in this article. Water is not absorbed across a simple membrane passively — rather, the small intestine is a two-layer barrier with specific transport proteins positioned in each layer of the barrier in order to pull nutrients into the body at a very high efficiency.

A dominant theory right now is that sodium-glucose co-transporters are responsible for drawing water into the body (see http://www.ncbi.nlm.nih.gov/pubmed/16322051 and http://en.wikipedia.org/wiki/Sodium-glucose_transport_protei...). Specifically, an osmotic gradient is created by (I think) the Na/K active pump ("active" meaning the body uses up ATP to overcome the normal steady state). The Na/glucose co-transporter then uses this gradient to pull those molecules into the body, bringing water with it — the water of hydration.

If we were hydrated using a simple system such as the one depicted in the link, we would be orders of magnitude more responsive to the food we eat. Our bodies are very good at maintaining homeostasis, but it takes a lot of complexity to do it.

Edit: it's worth noting that seawater may indeed be too highly concentrated to drink safely, even in moderate quantities, if it's true that the kidney cannot excrete at a greater concentration of salt as is present in seawater. This link from Wikipedia suggests this is the case: http://www.newton.dep.anl.gov/askasci/bio99/bio99416.htm . But the posted article's explanation is entirely off-base in its explanation regardless. And I'm not even sure what of seawater would be absorbed on an empty stomach...it's possible more salt than water would be absorbed, leading to diarrhea as water is left unabsorbed in the intestine, leading to dehydration from poor water absorption and poor salt excretion.

icegreentea• 15 years ago

Well, to be fair they are talking about sea water, which has an approximate average salinity of 35g/L [1]. Gatorade (reading off the label from the bottle sitting on my desk) has 110mg of sodium and 30mg of potassium per 240mL, so about 600mg of 'salt' per liter. There's ~60 times more salt in sea water than Gatorade.

We are actually pretty good at maintaining homeostatis. But it's really hard to deal with the amount of salt in sea water. In addition, you and the article are not actually going over the same thing. The stated problem is not during absorption (which you deal with), but what happens after you absorb the salt water.

[1] http://en.wikipedia.org/wiki/Seawater

jforman4• 15 years ago

"The stated problem is... what happens after you absorb the salt water" — other comments about this paragraph notwithstanding, it's just not true that simple osmosis from blood to cells is the operative factor in hydration, so the article is totally off-base. You can't talk about hydration without talking about intestinal absorption and concentration of urine in the kidneys.

todsul2• 15 years ago

Did you bother reading the article?

  > Alas, this article is not remotely accurate.

I'd like you to qualify this. "Not remotely accurate." Do you suggest sea water is a remedy for dehydration. Or are you suggesting osmosis doesn't occur across cell membranes. Or maybe you're disputing the process of osmosis altogether and the transfer between varying salinities. Which one is it exactly?

The article is talking about the dangers of drinking sea water when severely dehydrated if stranded on the coast or at sea. You can't extrapolate the sodium in Gatorade to drinking straight sea water. That's not only haphazard, but completely irresponsible considering we're discussing health and survival.

Also, the images depict cells all over the body; not just in the small intestine and certainly not villi.

Sure, this isn't the most robust explanation of a bodily function. This is an expedition travel website. It's not the Journal of Medical Science. The purpose of the article is to stop people drinking sea water as a remedy for dehydration. As some people have mentioned, small controlled quantities may help. But when you're that delirious, I can't help but think even having that thought in your mind would cause more harm than good.

jforman4• 15 years ago

Yes, I read the article.

"Do you suggest sea water is a remedy for dehydration. Or are you suggesting osmosis doesn't occur across cell membranes. Or maybe you're disputing the process of osmosis altogether and the transfer between varying salinities. Which one is it exactly?"

I just mean this: whether seawater causes dehydration in small quantities is a complex question, one which reading this article will provide absolutely no insight into.

"You can't extrapolate the sodium in Gatorade to drinking straight sea water. That's not only haphazard, but completely irresponsible considering we're discussing health and survival."

I never said that seawater is hydrating? Seawater lacks glucose and may have too high a salt concentration to promote hydration even if it did contain glucose. My apologies to anybody who misinterpreted my post after finding themselves stranded on a desert island.

"Also, the images depict cells all over the body; not just in the small intestine and certainly not villi."

The images are clearly presented in such a way as to suggest that simple osmosis between cells and seawater-containing blood is the operative factor in determining hydration. This is totally untrue.

"Sure, this isn't the most robust explanation of a bodily function. This is an expedition travel website. It's not the Journal of Medical Science."

That doesn't give them license to just make stuff up.

ahoyhere• 15 years ago

Lots of people have died from drinking sea water. It's still a Very Bad Idea. Your argument is along the lines of "They got technical details wrong; salt water is sometimes important; therefore the whole thing is wrong." But that is like saying the advice to "Do not handle rattlesnakes" doesn't apply because some folks get a great deal out of handling rattlesnakes. The fact is, people who don't know what they're doing shouldn't handle rattlesnakes… or drink sea water.

Now let's talk about oral rehydration salts -- the non-fancy name for the salt water and "glucose transporters" you described.

The salinity of Oral Rehydration Salts/Solution is nowhere near as high as sea water -- and without the sugar, saltwater doesn't rehydrate. The formula for making it yourself is about 1/2 tsp salt in a liter of water, plus 6 tsp of sugar. That's a lot of sugar to balance out just a little salt: 1:12 ratio.

A quick Google suggests that 35g of salt is what one would expect in a liter of sea water (on average). A tsp of salt weighs 5.7 g. Therefore, the concentration of salt in sea water is 6 teaspoons vs 1/2 tsp in ORS, or 12x the concentration of salt.

And no sugar.

I drink ORS on a regular basis to deal with one of the side effects of chronic fatigue syndrome: an imbalance of hormones in the body which leads to insufficient electrolytes which leads to POTS (postural orthostatic tachycardia syndrome), dizziness, muscle cramps & twitches, brain fog/inability to think straight, and inability to drink adequate water.

ORS has been a total life changer for me -- before, doctors just said I was "too out of shape" when sitting up/standing led to a doubled heart rate, dizziness, the feeling that "the bottom dropped out of my head", near fainting, etc. Because that's a valid explanation when a 27-year-old nearly passes out from standing up. (Not.)

Drinking a little salty-sugary solution solves my symptoms in 20 minutes.

But I sure as hell wouldn't drink sea water.

mikeash• 15 years ago

The article is titled, "Why Can’t We Drink Sea Water?" The technical details that they got wrong are the whole point of the article, and it is completely reasonable to complain when such an article is inaccurate.

kragen2• 15 years ago

If you put the same amount of salt in the same amount of water without the sugar, it will still rehydrate you. Just not nearly as fast, because it's being absorbed only by the osmotic mechanism described in the article instead of the sodium-glucose co-transport mechanism described in the comment by jforman you're replying to. Half a teaspoon per liter is roughly isotonic, so as the salt is absorbed through your intestinal wall (slowly, through diffusion), so is the water.

I concur with the other poster who said that the technical details they got wrong are actually the whole point of the article.

Thank you very much for relaying your experience with rehydration solution! I had no idea.

DevX101• 15 years ago

If I were a professor and the question was "why we can't drink sea water", I'd give the article a higher score than yours.

Your comment is about the best method to hydrate oneself. His article is about "why we can't drink seawater".

ars2• 15 years ago

It might be about that - but it's wrong. The obvious proof is that Penguins and Fish can drink sea water.

At least the comment was correct, although about a somewhat different subject.

dbbo• 15 years ago

Maybe I'm just biased because of my curriculum, but I didn't find this article informative at all. I actually found it overly dumbed-down. Perhaps it was meant for people with zero biology/chemistry knowledge.

donw• 15 years ago

Although only moderately related to the article, it's worth noting in this situation that the ocean could still be of use to you in maintaining water levels.

Arid climates are dangerous because they force us to sweat in order to maintain body temperature, at a rate between 1L and 2L per hour, depending on how much you're exerting yourself.

While you can't drink the water, you certainly can use it as a heat sink. Taking a bath and soaking your clothing in the water will both cool you down and assist in the same evaporative cooling process, reducing the amount you need to sweat.

Coupling extra evaporative cooling with limited movement during the day will help you conserve a lot of water, and could extend your survival time by more than 50%.

anateus• 15 years ago

If you have only a smaller amount of fresh water, it is possible to survive with little ill effects if you mix fresh and salt water in a 2:3 ratio (respectively).

http://en.wikipedia.org/wiki/Seawater#Human_consumption_of_s...

abeh• 15 years ago

A university biology professor mentioned in a lecture that a small percentage of people have kidneys strong enough to drink sea water.

error• 15 years ago

it's very salty :)

kragen2• 15 years ago

http://www.straightdope.com/columns/read/2131/what-would-hap... has somewhat more in-depth and better information on the topic. This article is disappointing.

S_A_P• 15 years ago

I saw an episode of "Good Eats" that Alton Brown discussed this. He stated that an 8:1 ration of fresh - sea water could be used to extend water supplies as well as make your body retain the water longer so less is needed vs pure water. I would be curious to know if this is a good ratio, should I ever become shipwrecked :)

Why Can't We Drink Sea Water?

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