Introduction: How to Desalinate Seawater

Picture of How to Desalinate Seawater

I can't believe there's a whole ocean full of water but we can't use it.So here's a way to desalinate seawater.It is best to try it on a sunny day early at sunrise;it will be done more or less in the afternoon.

Step 1: Prepare the Container

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Use the big container and put the round black lid inside it.This is to atract sunlight.

Step 2: Add Recepticle

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Place the small cup in the middle of the container on the black lid.

Step 3: Add Saltwater.

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Add some seawater that you want to desalinate in your container but don't spill it in your cup.

Step 4: Cover With Plastic

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Put the plastic over the container and fasten it with your elastic band.

Step 5: Small But Very Important Modification.

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Add a small weight on the plastic right above the cup so that the plastic points down to your cup.

Step 6: Wait.

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Wait for the water to evaporate, condensate on the plastic and trickle down and into the cup for you to drink.


PatrickC177 (author)2017-11-10

i will try this if right well this can be a very money saveing for me

muddywateroutfitters (author)2017-06-24

Definitely a useful tool in a survival situation, but a solar still isn't something I would recommend solely relying on for water in a survival situation. They take a long time to purify a comparatively small amount of water and you're more likely to end up with far less water to drink than you expend over the course of waiting for it.

A relatively simple way to expedite the process is to use a double boiler over a fire made of two metal containers ( you can substitute soaked birch bark cups or leather hides in an outdoor emergency, or really any container that won't burn or melt. ) and any sort of cone ( again, whatever yo can come up with. ) that you seal to the container with whatever you can find to keep the steam from leaking. By putting the whole deal over a fire, you will lose some evaporation through the seams in your makeshift still, but the increased efficiency of the whole thing will more than make up for it, with the added bonus of giving you a warming/signal/cooking fire to work with through whatever disaster you find yourself in.

Awesome. Do you think you could do an instructable showing this process. And i have a simple question. Can you drink rain water collected or would it be wise to filter that as well. Thank you for your response

Drinking rain water should usually be safe, but if you have the ability to distill or purify it, you should still do so. While it will generally be "clean" of pathogens, it does collect some level of dirt and other impurities like heavy metals as it falls to your collection vessel and in a survival situation, you're not going to be sure that your collection tools are clean. So while you can drink rainwater without a big risk, the number of things it contacts between falling out of the sky and going into you can result in potential sickness. Part of the point of purification that's often overlooked in discussion and survival guides is that you're not only purifying your drinking water, but also purifying the container you're drinking out of.

You can't always afford to make fire, in survival situations.

Nikiniku (author)FlorinJ2017-06-27


I don't understand. Do you mean that the enemy might find you?

I believe he's referring to situations like being stranded at sea, or similar where fire would be either too difficult or dangerous to make, but those sorts of situations are VERY far and few between. As a rule, a fire is one of the best things you can have under survival conditions for a variety of reasons.

Yes i completely agree. But. And this of course is a big but. If you were in end of times say and it was all out anarchy. She makes a valid point. What would be a trick for a fire to do the water desalination and keep the fire hidden. IE no smoke no signals that i dont want people to see that im there and have supplies for you to kill me for. Far fetched but valid.

Here is something that I was taught in the survival course when I was in flight school: 1.) In beach situations find the high tide mark, 2.) Pace off 100 "yards" inland from that point, 3.) Dig down into the soil until you hit "water", 4.) Collect that "water" [it should only be a ~.5% to 1% saline solution (normal salinity is 3.5%)], 5.) Filter that collected water through any piece of wadded up cloth, 6.) Then if possible construct a solar still using that "water", 7.) Your solar still will be much more efficient & the untreated water can be used for cooking and personal hygiene.

P.j.N (author)ewbray2017-06-27

Awesome response. Taking notes my friend

ewbray, that's absolutely a good addition wherever possible. Anything that helps with reducing the amount of energy and time expended in purifying your water is a technique worth adding to your mental tool kit.

M.D5 (author)2017-07-23

I saw a documenrary from Australia when I was a kid, Henry Butler's In the Wild, where he showed this in the outback. Not that I could use it here in Europe, but it impressed me non the less. And recently R Redford did it in the movie All is lost (great movie for sailors btw).

rhetoricmonkey (author)2017-07-18

I found an article that confirms this can be done. Thanks for the instructable.

Chimonger (author)2017-06-28

Once the water has been condensed and captured in a jar, put a lid tightly on the jar, and let that sit in the sun to cook it, to kill pathogens/parasites. Of course, this requires planning ahead, and having multiple jars to cycle through the process.

Could make a tray with glass over it, and have the condensate run downhill into a catch-trough inside the tray, which runs out a drain into a container, to make more clean water per batch. If you use glass containers to store the water, it can be heat-purified by tightly lidding the jars and putting those in the sun to heat up. OR, use emergency small-branch filters from trees and shrubs that have longitudinal fibers, and are non-toxic....use the stick to plug the bottle of water, turn that upside down over another container to let gravity filter the water through the stick, to remove parasites and germs. One-time use per stick.

JoãoP142 (author)Chimonger2017-07-13

I don't see why we should do that. The condesated water it's a clean one.

Chimonger (author)JoãoP1422017-07-14

It would be nice if we still had clean rain.
But we don't...almost anywhere in the world now, it's contaminated by various heavy metal particles, as well as chemicals, one way or another.
During distilling, be it solar or boiler method, much of the particles, germs, and chemicals remain in the cooker.
BUT...there are still some hazardous chemical residues of certain kinds, that are small enough, light enough, and bond with water well enough, that they travel along with the steam or condensate, into the collection bottles.
Therefore, it's important to, at the very least, use an activated charcoal filter on the distilled water, to make it fit for potable use.

JoãoP142 (author)Chimonger2017-07-15

That would only be necessary if those chemicals had a close ebulition temperature at the same pression as water. I don't know, maybe there is.
The chemicals that are dragged by the rain, as you mentioned, were already in the atmosphere. I don't have knowledge of a chemical bounding to water, in which would mean a chemical reaction, but it would be no longer water, nor sharing its propertys.

I do understand your point of view, there could lots of contamination sources, including the cup itself. But you should understand that evaporization means that the molecoles of water are free, not bounding to other chemicals. If some of those chemicals also evaporate, it would be minimal in comparassion with the salinated water.

square egg (author)Chimonger2017-06-29

Chimonger, letting it 'sit in sun, to 'cook' will NOT kill the pathogens / parasites. On the contrary: like with most pathogens / parasites, the warmth will only make them flourish. (Basic logic: If they weren't 'cooked to death' under the sun, while in the sea - why would it be any different while being under the same sun, in your garden)? If you want the water to be sterilised and parasite free - it needs to be boiled.

Chimonger (author)square egg2017-07-14

Closed container in the sun, can result in water that can cause a blister. That's hot enough to kill pathogens. Caveat: Allow contents to solar-cook long enough, to kill the pathogens. I'd give an educated guess, that once the contents are too hot to touch the jar, leave it for at least 1 hour.
The sea is a huge open volume of water. By your 'logic', solar cooking would never work....except solar cooking is real, and has been real for a very very long time. If one can heat liquid in a closed jar, hot enough to blister skin or flat-out boil it, it can kill pathogens.

mikeA135 (author)square egg2017-07-14

Really,logic.....The sea is an enormous body of water which takes a lotttt of heat and time to warm up, it's not the same logic as a small container in a garden at all. Same sun, different volume. I would tend to agree that evaporation should be fine, water molecules are separate more or less in a gaseous state and would not act as a medium to transport bacteria etc. Although perhaps cross contamination from the surface it is condensing on could occur.

pvdelg (author)square egg2017-07-04

as noted this is a process of evaporation, all the pathogens including viruses will not float out of the water with the evaporate and condense again in the collection bottle, the water will be perfectly safe without boiling.

Chimonger (author)square egg2017-06-29

If one leaves the lid off, the contents cannot heat up. If the closed bottle is not left in the sun long enough, of course it won't get hot enough. But, IF the bottle is closed, And in the sun long enough, it cooks the little beasties. ....Same reason you don't leave a pet or child in a car on a sunny day [some places, even in winter!], because the interior gets too hot to live. ....Same reason greenhouses get warm and keep warm, if in the sun...and need vented on sunny days, to avoid killing the plants inside from over-heating [depending on greenhouse and other weather conditions].

DaveM125 (author)square egg2017-06-29

Water captured via evaporation is already pure as pure can get unless your container or plastic is contaminated.

square egg (author)2017-06-30

Thanks for your reply, but, in response to your points:

1. Keeping the lid on the bottle/jar will only prevent the water from evaporating, but will not make any difference to the process of 'killing' the 'beasties inside the water.

2. The examples you gave (over heated plants in a green house, kids and pets in a closed car on a hot day) - are perfect examples to CONFIRM MY POINT... :-)
Like all living things - different beings can survive different conditions, or die in different degrees of heat.
Sensitive green house plants, young kids and pets might die if exposed to about 50 degrees for a few hours, but bacteria, pathogens / parasites and most other 'beasties' - will not.
(Think of a sandwich you forgot in this locked car in the scorching sun: the mould on it will only multiply and flourish faster in this 'lovely warmth', but your flowers next to it shrivelled and died.
Also: Your car will not turn 'sterile' or 'germ free' due to the scorching heat in the parking lot)...
50-60 degrees of heat are just not sufficient for that, and this is why the water HAS to be BOILED: Given the full minimum of 100 degrees heat... :-)

NikyN2 (author)square egg2017-07-04

actually, I heard once (on a serious site), that an easy and cheap way of getting safe water (for 3rd world countries, mainly) was to fill plastic bottles and let them sit in the sun for a few hours. the heat (and probably the UV too) makes the water clean enough for human consumption. the temps reached only 50ish C, btw (or the bottles would have melt).

so, yep. both moderate heat and UV can make water safe. and tbh, the guide exposes the water to both, so, it SHOULD be safe.

also bacteria thrives best when close to human conditions. I don't think 50C will kill them all, but they won't be growing that well under such extreme conditions. 35C on the other hand.... the perfect petri dish (and btw, you'd be surprised how easy is to reach 50C under direct sunlight - in summer, of course).

Lovetra (author)2017-07-03

This discussion is funnnnnny about galvanized buckets. Yeah! Back in the day, we used them, (GALVANIZED BUCKETS, WASH TUBS, ETC), EXTENSIVELY. OF course I am talking about generations born prior to 1945, living on farms and or still in some log cabins and shacks in the boondocks. A lot of us (generation prior to WWII) didn't have fancy cars, some still rode horses, many roads other than main highways were gravel grated roads with a grater to fill in mud holes. and we pumped water with a pitcher pump or carried it from the creek. I never heard of someone going to the doctor or hospital with zinc or galvanized poisoning back then. We pumped the water, heated it over open fire, washed our dishes,our clothes and took baths in it!

To this day I have a 2 gallon galvanized bucket with a tight fitting lid I store my flour I buy in a 25 lb sack for baking. No bugs, no moisture, no spoilage and good biscuits! Any passage of toxins is minuscule I guess cuz' so far I have never poisened anyone.

Now if you are going to get it hot enough to melt with a forge or high power torch your talking about totally different and higher quantities with gaseous fumes floating in the air consumed by breathing in.

Putting galvanized nails in ones mouth might be toxic if they do it on a daily basis for several hours a day.

I listen to some of this crap and wonder how my generation ever survived?

Nice to know how to separate salt, even small amounts from sea water. Shows why they say it is so expensive to do to supply a whole city with fresh water.

Kevanf1 (author)2017-07-03

Another way of getting drinkable water to supplement this is the plastic bag and bush method. Get a plastic bag and place it over a bush that has plenty of green leaves on it. Wrap the open end of the bag (not too tight as there is no need) and then make sure one corner of the bag is hanging down. Over a period of a few hours moisture (drinkable/potable water) will collect in the lower corner of the bag. This is ok to drink. You won't get a massive amount of water but any is better than none in a survival situation.

WilliamB382 (author)2017-06-27

put the water in a galvanized bucket and apply a little heat to the bottom should speed up the process. (Black lid would have to be removed or made of non-plastic)

P.j.N (author)WilliamB3822017-06-27

Wouldnt the galvinization be a factor in the purity of the water. Im a carpenter and have been told to never put galvinized nails in my mouth. Look forward to your answer as i am clueless about which it true

Garyzzzz (author)P.j.N2017-07-01

zinc is not toxic but some screws, nails are cadmium plated and Cd is toxic.

KatB21 (author)P.j.N2017-06-28

No, because the water is evaporating then condensing on the plastic. The zinc used for galvanising the bucket will stay behind in the same way the salt does.

Putting galvanised nail in your mouth won't actually do you any harm, some of the zinc will react with the acid present in your mouth, but zinc is not harmful in any form.

AlphaOmega1 (author)KatB212017-06-29

nstvstv (author)KatB212017-06-28

Zinc is highly toxic in fume form, for instance when welding galvanised iron or steel; or at temperatures above about 450 centigrade, which may be attained by coke or charcoal burning in galvanised containers.

Chimonger (author)P.j.N2017-06-28

Galvanizing out-gasses when heated. It outgassed into certain fluids [hence, don't put those in your mouth!].

Poppy Ann (author)P.j.N2017-06-28

Most older houses were fitted with a zink galvanised cold water tank so i doubt holding a few nails in your mouth would do much harm to you unless you started to swallow them.

Chimonger (author)WilliamB3822017-06-28

NO! Galvanizing chemicals out-gas when heated!

You'd be better off using a black plastic bucket. Or even a hole in the ground with the cup and weighted plastic. OR filtering the condensate using a small section of woody branch of a non-toxic tree to drip-filter it through.

Tenebrax (author)WilliamB3822017-06-27

I'd be REALLY careful about heating a galvanized container. Heating galvanized metal beyond a certain temp gives off extremely toxic fumes, and why bother removing the salt from the water if you're going to add poison?

and7barton (author)Tenebrax2017-06-27

Not especially toxic. You are getting it confused with lead. Inhaling the fumes from very hot zinc will give you a bad headache at the worst. I've suffered this a number of times as my profession involves cast molten zinc and other metals. It's a minor inconvenience. Unlike lead, Zinc is not retained by the body and is soon eliminated.

k5cqb (author)and7barton2017-06-27

While this setup would never tolerate the heat required to burn zinc the fumes from burning zinc are extremely toxic. Look up the case of Jim "Paw Paw" Wilson a famous blacksmith who lost his life to Zinc Metal fume Fever

spark master (author)Tenebrax2017-06-27

ZInc fumes will come off at a temperature that is so very high the plastic cup inside the bucket will be a soot spot inside the totally empty, devoid of liquid, steel pail.

Zinc poisoning is not happening, in a a gently heated bucket of water. Think RAGING BARN FIRE.

WilliamB382 (author)WilliamB3822017-06-27

Forgot, you would need a concave surface instead of plastic cover like an upside down sauce pan lid

terrynight (author)2017-07-01

I agree: there is an abundance of water and we should stop believing what they force-feed us! As a fellow Capetonian, I cannot believe how many sheeple live here and actually don't want to challenge the norm. Let us make our own water supplies and share ideas on how to do it safely, efficiently! Good GOING!!

cdavenport (author)2017-06-27

Excellent demo/concept. To increase the amount of desalinated water collected, one need only increase the wetted surface area. Also, your technique is applicable to purifying run-off water, ground water, or dirty water. One needs only a depression in the ground, a collection cup, and a larger sheet of plastic. The process works without the sun if the temperature is suitable albeit at a much slower rate.

LavonneW1 (author)cdavenport2017-06-27

Technically it will still not be "pure" water. The process will not kill bacteria and other baddies, it only removes particulates, minerals, etc.

DawnS48 (author)LavonneW12017-06-28

If the plastic is clean no bacteria or other baddies will transfer to the cup

Ziggy_Mondus (author)DawnS482017-06-30

Exactly :)

Ziggy_Mondus (author)LavonneW12017-06-30

This method, as in ALL distillation processes, evaporates water into the air and the water condenses onto the plastic sheet, therefore leaving ANY bugs, germs, bacteria, - and salt - in the original place.

It does not matter if the bugs survive, they can't fly. So as long as the condensing sheet and receiving vessel are clean - so is the water.

LindsayF10 (author)LavonneW12017-06-28

LavonneW1, I see cats drinking water out of the birdbath all the time.. :)

but it causes them pain to do so...why else would they say me-ow

Ha ha! ;-D

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