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Why Can't We Drink Sea Water?
- iwwr 15y agoKidneys like marine mammals have could help us. Relevant: http://www.scientificamerican.com/article.cfm?id=how-can-sea-mammals-drink http://www.scientificamerican.com/article.cfm?id=how-can-sea...
- dpcan 15y agoThis 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 15y agoIn 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...
- iqster 15y agoThey have desalination plants in the middle east. The problem with those is that they are very energy intensive.
- latch 15y agoThe pacific is worth mentioning too...Singapore in particular, and Australia increasingly so. A handful of southern US states are getting things ramped up too.
- mahyarm 15y agoI think solar heat desalination plants in very hot climates like that could be more practical. +40C is fairly common in Singapore and the Middle East
- dalke 15y agoAnother problem is the output flow is more saline, which affects sea life.
- jonknee 15y agoThere's a large desal plant in Florida too, it supplies part of the water that I drink. You're right in that it's energy intensive, but at least in our part of the world the largest problem was water quality. There's a lot of biomass floating around in sea water and it means having to constantly repair the filters. I believe there was a big issue with an invasive species of mussels as well that do quite a bit of damage. http://www.tampabaywater.org/facilities/desalination_plant/index.aspx http://www.tampabaywater.org/facilities/desalination_plant/i...
- Roboprog 15y agoThe 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 15y agoEvaporation 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 15y agoThe 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.
- bch 15y 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.
- gnosis 15y ago"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." Take a look at: http://www.finishing.com/156/65.shtml http://www.finishing.com/156/65.shtml My favorite quote from that thread: "If it is a concern & all you have to drink is ultrapure water, you can stir the water with a metal stainless spoon or your finger first & it will magically transform itself from ultrapure water to just water."
- bch 15y agoThanks for the link, but not very convincing. The site itself is a forum for the metal finishing industry; like chrome and silver plating, not something I'd hold up as expert in human health and diet. Most of the discussion oscillates between "Yes it's harmful. If you want to consume DI water that does x, do so at your peril." and "No it's not harmful. Why are you afraid of something we already use for x?"
- latch 15y agoNot 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 15y agoSuch 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_chester 15y 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.
- bdonlan 15y agoYou could purify and sell the salt as table salt, etc.
- pacaro 15y agoGiven that there is a commercial market for sea salt, dumping it back in the sea would seem counter productive...
- jacques_chester 15y agoDesal plants produce prodigious amounts of salt. Some of it can be sold, but not all of it. You still wind up with piles of the stuff that need to go somewhere.
- deleted 15y ago[deleted]
- Someone 15y agoUnless you are doing this on a scale that (almost) literally boils the oceans, I doubt that really is a problem. The oceans are _big_, and not that salty. Also, as another comment already said, you might be able to sell the salt instead.
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- todsul 15y agoDefine 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-jamaica-mexico http://globetrooper.com/caribbean-sea-row-2012-barbados-jama... Katadyn does desalinators for civilians. http://www.katadyn.com/usen/katadyn-products/products/katadynshopconnect/katadyn-desalinators/ http://www.katadyn.com/usen/katadyn-products/products/katady...
- carsonbaker 15y agoFor 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-didos-watermaker http://www.albin25.eu/our-a25ak-dido/34-dido-stories/60-dido...
- acangiano 15y agohttp://www.thewatercone.com/Index.html http://www.thewatercone.com/Index.html
- jerrya 15y agoBased on a solar still, http://en.wikipedia.org/wiki/Solar_still http://en.wikipedia.org/wiki/Solar_still, there is the Water Pyramid for villages, http://en.wikipedia.org/wiki/Water_Pyramid http://en.wikipedia.org/wiki/Water_Pyramid and the Water Cone for personal use: http://www.thewatercone.com/Index.html http://www.thewatercone.com/Index.html
- Panoramix 15y agoThere'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/ http://saltworkstech.com/
- hugh3 15y agoDesalination 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 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%
- iqster 15y agoI 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 15y agoThanks, 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_chester 15y agoFor 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 15y agoI'm surprised I was never taught this before. Great post.
- carsonbaker 15y agoThis is controversial, but Alain Bombard (http://www.nytimes.com/2005/07/24/obituaries/24bombard.html 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/thirst http://naturalhistorymag.com/picks-from-the-past/181950/thir...
- Loic 15y agoA 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 http://en.wikipedia.org/wiki/Alain_Bombard
- electromagnetic 15y agoActually 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 15y agoWouldn't it be more pleasant to drink fresh water and take salt pills separately?
- ghshephard 15y agoIt's difficult for me to drink fresh water in large quantities (more than a liter an hour) but when I put electrolytes in them, I find I can drink somewhere on the order of 2x to 3x more. I buy these 100 at a time - seems to do the job pretty well. http://www.hydrationdepot.com/Qwik-Stik.html http://www.hydrationdepot.com/Qwik-Stik.html
- BerislavLopac 15y ago
- philfreo 15y 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 15y agoYou'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 15y agoI 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...
- mseebach 15y agoStrictly 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.
- oelewapperke 15y agoThat's true, of course, but he did go far above what a normal being can take : you should not drink more than 1 liter of water per hour, because your kidneys can only remove that amount of water per hour. If you drink too much water (> 90ml/kg is LD50, the dose 50% of people won't survive, so for a normal adult of 70kg we're talking 6,5 liters of water as fast as you can chug it in), the electrolyte balance in your nervous system will reverse, eventually resulting in the depolarization of all axons. Since this doesn't occur at all places in the nervous system simultaneously it will be a very painful and extremely scary way to die. Anyway the doses the GP mentioned are enough to create issues (anything > 1L/hour creates issues, and a sustained water intake of more than 1L/hour will eventually kill you)
- russell 15y agoReverse 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 15y agoReverse 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 15y 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 15y agoBut why cells are so finicky about salinity? Why can't cells operate properly with some salt present?
- oelewapperke 15y agoThe basic reason is energy. Osmosis is free, energy-wise, as it lowers the entropy of the system as a whole. So basically water intake through osmosis doesn't require any energy, whereas any other method would require massive amounts of energy to fight the osmotic gradient. It would also mean that every other cell intake would have to use active transport. Long ago evolution decided that regulating water intake would be too expensive, and so we don't. (which is also why it would be a horrible idea to try to cool down in sea water if you're dehydrated. Don't do it ! And for the love of God, don't get any of it on your face) You can make fresh water out of sea water using just a sheet of plastic and something to catch the water. First, dig a hole in the ground, in a piece of sand that was exposed by ebbing water. Say 20-30 cm deep. Put a cup in the middle of the hole on a stone. Wet the sand with seawater, put the plastic over the hole, attaching it to the sides somehow and put a stone in the middle of the hole. Water will evaporate, hit the plastic which will be slightly cooler than the air below it, so part of the water vapor will become liquid, go towards the middle where you put the stone, where it's cooler still because it's deeper in the ground, and it will drop down into the cup. For better performance, you can put anything that contains water, like plant leaves, rip them to pieces and put those pieces under the plastic. But sea water will work. This is not good enough to remove all salt, but it will reduce it significantly. And btw, if you need to cool down : dig a hole deep enough to have permanent shadow, and lie in it.
- jforman 15y agoAlas, 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 http://www.ncbi.nlm.nih.gov/pubmed/16322051 and http://en.wikipedia.org/wiki/Sodium-glucose_transport_proteins 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 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 15y agoWell, 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 http://en.wikipedia.org/wiki/Seawater
- dbbo 15y agoMaybe 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 15y agoAlthough 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 15y agoIf 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_seawater http://en.wikipedia.org/wiki/Seawater#Human_consumption_of_s...
- abeh 15y agoA university biology professor mentioned in a lecture that a small percentage of people have kidneys strong enough to drink sea water.
- error 15y agoit's very salty :)
- kragen 15y agohttp://www.straightdope.com/columns/read/2131/what-would-happen-to-you-if-you-drank-seawater 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 15y agoI 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 :)