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  1. #1
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    Question Making an efficient still for drinking water

    I saw the thread on making an emergency still for making drinking water, and got thinking. How hard would it be to make a water purifying still out of an old pressure cooker? And I mean only for making drinking water.

    I have a pressure cooker I am getting ready to dispose of. If I yake the pressure cooker fill it with water and not put the weight on it but connect the stem for the weight (for lack of a better name) to a cooling coil to condense and collect water. Of course this would be after boiling the water 5 or 10 minutes to remove solvents like I read somewhere. Would that make an efficient still to make drinking water?

    As long as it is venting through the coil it should not become a bomb, right?

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  2. #2
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    Distilling anything requires precise temperture control ... not everything that polutes water boils off below the boiling point of water.. some stuff boils at higher temps ... while water is boiling, if water is the main part of the liquid, the water, by boiling, keeps everything at 212 degrees.. but as the ammount of water is reduced and any polutants by concentration start to become a sizeable fraction, the boiling point can change, with the extreme case being boiling a pot dry and anything that boils or turns to vapor will, when it reaches that temperture point, goes up with the water.. leaving only the minerals in the pot or kettle that have a higher vapor point than you can get on a stove .. 400-500 degrees or so.

    You want just water, you control the temp a close as possible to 212 degrees, or you only boil off about half to two thirds of the liquid .. you never let it boil out dry. This is on top of driving off anything with a lower boiling point by letting the steam escape for the first 10 minutes of so of boiling.

    That means recovering maybe half the liquid you started with... that is not what I call efficent, especially when you may have to chop wood or gather deadfall for fuel.
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  3. #3
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    Just to add a thought, and a practical example...
    Sea water, althought it varies in salinity in some places around the world depending on how many rivers locally empty into it basicaly has 3.5% disolved solids in it ... and has a Boiling point of 218.66 degrees instead of 212 degrees like pure fresh water. The Mediterranean Sea is at about 5% and has a boiling point arround 222 degrees farhenheit. So as poluted water boils down some unwanted stuff can also get boiled off. Here are a couple of canidates http://en.wikipedia.org/wiki/1,4-Dioxane , http://en.wikipedia.org/wiki/Toluene, and http://en.wikipedia.org/wiki/Formic_acid. and if that is not enough, 1,4-Dioxane has a specfic gravity of 1.03, water being, of course, 1.0. And the stuff that doesn't boil off will increase in concentation, further increasing waters boiling point, and adding other chemicals to the steam like http://en.wikipedia.org/wiki/N-Butanol and http://en.wikipedia.org/wiki/Acetic_acid.

    Where it gets wierd and complicated is water is pretty unique in it's properties .. high specific heat capacity and high heat of vaporization, but like all liquids it's boiling point increases with increasing pressure and decreases with decreasing pressure... so since different chemicals change in the same way, but at different rates, the list of chemicals that boil at or very near the same tempertures as water may vary based on altitude or if you boil water under pressure , like a pressure cooker with the weight off but that is producing more steam than can get thru the vent at standard atmospheric pressure..( ie shooting a jet of steam).

    Just saying... it may take a few more steps to chemically remove the dangerous things that just stove top or campfire boiling can't seperate from water.
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  4. #4
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    Okay, so this is an over simplified solution to the problems you have stated, but the use of a charcoal filter, wouldn't that remove the collected chemicals? It seems to me that running the condensed water through a good charcoal filter would supply the necessary area surface and contact time the filter would need, right?

  5. #5
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    Nothing that requires a working heat source and/ or fuel is going to be simple in a shtf situation.. it's a hassle to collect or carry fuel, takes up space in a vehicle, locks you down to a fix position while you process water , and has a heat, flame, or smoke signature.

    Just as an example a full sized Berkey weights about 10 pounds, is self contained, needs no power source and can filter 6000 gallons of water ( about 50,000 pounds or 25 tons) at about 100 gallons ( 830 pounds) a day max , if for some reason you need that much, and it takes care of all the possible polutants ( a few drops of chlorine in the water before you filter it as insurance if you want). Boiling water , depending on your gear, can take anywhere from 1/4 pound of charcoal for the specialized designed chimney kettles to a pound of wood on an open fire.. without electricity you are looking at anywhere from 3/4 ton to 3 tons of fuel to just bring the water to a boil, twice that to boil it long enough to kill the germs/microbugs . To turn half of that gallon to steam for destilling purposes you need about 4 times that much fuel .. about 1 pound propane cylinder to convert 1/2 gallon of water to steam or 6,000, 1 pound propane cylinders or 2 to 4 Cords of wood @ 2 tons each or 3 -5 tons of charcoal depending on your systems efficency to equal the purifing power of a berkey with 4 filters installed. That doesn't sound simple to me. http://boards.straightdope.com/sdmb/...d.php?t=507216 I gallon of water is 8.35 pounds. 4.3 pounds of propane to a gallon or 93,000 BTU. Wood is about 9,000 btu per pound. Efficency of external heating of water is around 20% and you need 15,000 btu to boil off half of a gallon of water or 4 pounds of water.

    As to filtering the water thru charcoal.. forget it, it won't work... activated charcoal will work... but that is a different animal, and that is what most berkey or berkey like systems use. http://en.wikipedia.org/wiki/Activated_carbon http://www.buyactivatedcharcoal.com/
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  6. #6
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    If you need WATER
    you dig a good size hole in moist soil, add vegetation, urine etc, catch vessel, cover, with plastic (clear perfected) put rock over catch vessel, return at dark.... have a few and you are good to go.

    Charcoal filters can be made using CLEAN sand contained in a tin can, with layers of activated (or finely ground) charcoal, with a coffee filter or similar on the bottom to keep it all in.
    in the end it's about getting drinkable water, it ain't gotta be perfect, just not kill or disable you.
    Live, learn and be happy.
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  7. #7
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    The problem with make shift solar stills , aside from the already discussed issues with chemicals that don't destill out, this time the lower temp volitiles instead of the ones close to waters boiling point, is the quanity of water produced, if you start with just a coffee cup of poluted water, you are only going to get a fraction of that .. start with 8 oz like in the video and get maybe half of it ack as drinkable ... 4 oz out of a daily need of a gallon (128 oz) 32 cups and paper bags a day and you are good to go... the bigger tarp and rock thing is good for a pint, maybe a quart if you have good sunlight and live where humidity is high.

    http://wn.com/How_to_Build_a_Solar_S..._a_Solar_Still

    Love the guys " diplomas" from http://www.wildernesscollege.com/index.html heck, you can get half a dozen " diplomas" and 12-18 credit hours at the local community college in just 1 year and $9500 dollars thru Alderleaf Wilderness College and add those to your resume' too.

    A certified by the US Coast Guard and field proven solar still design with over 40 years of experience costing a couple hundred bucks only promises 1 to 4 pints a day.. http://www.landfallnavigation.com/me...mpaign=froogle better than nothing, especially when it comes to sea water.They do not work well unless you have direct sunlight.. if you concider a couple pints a day working well.

    Solar stills work, but clean water output is very small, well designed ones are expensive for the water you get, and they don't address polutants well .. temps may or may not get high enough to pasturize water ( 168 degrees ) for long enough to kill microbes.. certainly not cysts.. which is why they have limited application for land survival.

    I guess it all depends on what you concider efficent, and the quality of the water you will accept.

    I admit I have a strong prejudice about water and the concept of prepping, and getting the best possible water purifcation system , which also happens to produce the safest and least expensive water on a per gallon basis . the berkey, or a berkey clone , or even a do it yourself berkey using berkey type filters and plastic buckets.

    When the public utilitys go down and no longer process the water, we are going to join the rest of the world in the everyday reality that bad water is the world wide number 1 everyday killer of humans... and as bad as that reality is in the developing world, the addition of the industrial polution in the developed world on top of the consequences of poor sanitation in the third world when the water treatment plants here quit processing our sewage is going to make the witches brew that pass for streams and rivers here come home to roost.

    Clean safe water is just to damn important to leave to field expedient Russian Roulette makeshift measures that simply can't cover all the possible things that can kill you. When it comes to water, Yoda had it nailed .. "you either do or not do, there is no try"

    Just my studied opinion..

    If your plan A is to rely on field expedient measures.. at least try them out for real before the shtf , under realisitic conditions, with reliable stand by transportation that can take you to a nearby hospital in time to stop you from dying of dehydration from Diarreah in time.

    Even with all the advances of modern science and water treatment the local hospital sees several cases of Giardia http://en.wikipedia.org/wiki/Giardia and Cryptosporidium http://en.wikipedia.org/wiki/Cryptosporidium in otherwise healthy folks every year, just from contact like swiming in contaminated water. Also, don't take too much comfort that Crypto is most often found in AIDS patients... many things can make you immuno compromised, cancer treatments, artritis medications, steroids, asthma medications...if you read the links, be aware that some versions of the crypto spores are chlorine resistant or out right immmune to chlorine.
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  8. #8
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    The way the still works is by evaporating the water
    the point is that stuff like the salts and cysts DON'T EVAPORATE.....
    as for other pollutants, well it's cleaner than what you started with
    secondly, you set up a number of solar stills, you don't just dig one and that's it.
    And I have, a not that well sealed one relying on dirt moisture and the urine of 3 guys on a cool cloudy day made about a cup
    that surprisingly didn't taste like piss.

    Oh, and it's called an immune system, try to keep it up and it does wonders
    amazing what the human body can survive, look at all those counties with sewage in the water supply, and yet they DON'T all die off...
    parasites are survivable
    dehydration OTH well, that's fatal....

    as for a permanent source of water, the best bet is a clean supply, cause that about it, filtering is expensive, and requires consumables
    where do you put those in the bunker??? A good well or spring is worth many times more than any filter.
    Last edited by Mosinitis; 05-11-2012 at 05:32 PM.
    Live, learn and be happy.
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  9. #9
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    Actually filtering is the cheapest... $100 dollar set of black berkey's filter about 3000 gallons.. or about 3 to 4 cents a gallon... I have a rain catchment system that currently can hold 700 gallons and the local weather averages about an inch or so a week of rain, which provides 1200 gallons or so for each inch of rain... I'm going to be expanding that and installing a 1500-2000 gallon cistern to expand my storage capacity. I only need about 40 gallons of potable water a day, and I can filter 120 gallons per day for my group for drinking, cooking and cleaning and the occasional shower, bath rooms are on a septic tank and you can flush with straight rain water.. likewise water the orchard and gardens ( if they need more than what the rain brings). My filter system weights 10 pounds and is backpackable if we have to bug out, and can handle any contaminants.. plus everybody and every vehicle has berkey water bottles for emergency use good for about 75 gallons ( 1200 cups ) ..these , I will grant you are more expensive.. about 15 to 20 cents a gallon depending on the water. Berkey filters have a shelf life of 50 years so storing enough is not a problem.

    All in all, just carrying enough tarps to make enough water traps and solar stills is going to weigh more than about a half dozen berkeys... and If I need to collect dew off the grass in the morning, or from damp spots on the ground, I just use a shamwow cloth and wring it out until I have enough.. without all that digging and trying to use the shovel as a weight while I go find rocks and then waiting for somebody's piss to evaporate and collect on somebody's tarp that probably hasn't been washed or sanitized in the last 3 months, and just pour it all into one of the berkey sport bottles for proper filtering.

    $100 dollars worth of tarps and digging a dozen holes is going to get you what?, maybe a gallon a day, enough for one person, if you can find 12 likely spots to dig 12 holes everytime you move camp... and you can sit by the river watching and wondering if it is safe to drink while you wait for nightfall for a cup of water. That is cheaper?

    Well everybody's got a right to do things their own way I guess.
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  10. #10
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    Digging those holes is going to burn a lot of calories too. They have to be replaced or you will soon become too weak to dig the holes.
    Regards, Alan K.
    Available for Cabinet level positions, consultation on matters of foreign policy, weddings and bar-mitzvahs. Will work for gold or guns.

  11. #11
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    OK, just pointing out options (personally I'm all for finding a good spring meself)
    post a link will ya?
    Live, learn and be happy.
    Vic

  12. #12
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    OK, I see what's missing here. Enter Big Berkey in the search box and probably a dozen threads will pop up, including where they can be ordered for the best price. I think the same company that sells the grain mills carries them. Might be somewhere in the good deal alert sticky.
    Regards, Alan K.
    Available for Cabinet level positions, consultation on matters of foreign policy, weddings and bar-mitzvahs. Will work for gold or guns.

  13. #13
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    Cool

    we have more springs than i can count.....we used old pressure cooker in dear camps to cook fresh deer, foods
    as the fire was for heat it was used to cook too no burning of food or waste of energy .....

    after pressure goes up it will stay and go down as the fire go away or taken off heat will cook till pressures goes away cooling off!

    we boiled water too.....its whats you have.... not what you want to have that will be used first SHTF!
    as you have stated its cleaner than a lot of other countries in general will be safer than not using it at all...
    just remember not to flame your rubber around safety pressure bleeder.....
    add enough water to cook with the steam not burning food....(we used apple juice on the deer roasts)!

    good research SGT....VERY INTERESTING PRODUCT ANALYST.....things that get thrown it to products that have bad results.....like shampoos!
    Last edited by DK PHILLIPS; 05-16-2012 at 09:59 AM.

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