How well does boiling it work for removing contaminants, couldn't something be devised with coffee filters, metal screens and boiling that would make it drinkable?
Boiling works very well for living organisms.
Most everything from viruses up can be killed by roaring boiling for 12 minutes or more.
(5 Minutes at sea level, 1 minute longer for each 1,000 feet increase in altitude)
Boiling does OK on SOME chemicals.
Chemicals that have higher boiling point than water, it simply concentrates.
Boiling concentrates mineral, heavy metals, ect.
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Boiling in a 'Distiller', or 'Still' is the way to get most of the stuff out.
That will kill or remove all but the chemicals that can boil away and condense in the cooling chamber.
Boiling is very time consuming and takes up quite a bit of energy in the form of fuel for the heat source.
In the distilling process, the water becomes vapor, and leaves any of the solids, salts, parasites or what ever in the boiling chamber,
Then the water condenses and returns to liquid water again free of most problems in the water.
This is a VERY effective way to purify smaller batches of water, but it's too time consuming and materials consuming for large scale production for 'Survival' situations...
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Filters are a more effective in removing 'Particulate' or 'Suspension' particles.
That includes solids from minerals, chemicals, heavy metals and larger parasites.
Once the water is 'Clear' of solids were bad things and 'Critters' can hide, the easy and cost effective way to finish the purification is with Medical Grade UV light or with Chemical Treatment to kill the smaller bacteria or viruses.
In the 'Regular' world, particle filters are cheap and effective, and easy to buy at the hardware or discount stores.
In the 'Rough' large scale water filtration can be done by a few ways, including settling ponds or barrels, where the water sets long enough for the particulates to settle to the bottom,
Then through sand barrels to catch the really small critters and stuff with a specific gravity about that of water,
Then through Medical Grade UV light or chemical treatment before drinking.
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I'd also add 8 drops of bleach per gallon of water AFTER you boil it. It'll taste a bit like pool water (chlorine-y), but between boiling and bleach, just about anything living in it should be removed/killed. It should be at least safe to drink at that point, or at least better than Mexican water.
Actually, bleach and boiling do the same job...
Chlorine (active ingredient in 'Bleach) is there to kill the LIVING ORGANISMS, same as boiling does.
You could do both, but that would be over kill.
Adding a couple of drops of chlorine per gallon of water for long term storage would be a good deal to kill any 'critters' that try and get a foot hold while the water is stored...
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I have heard of half a t-spoon per gallon, is this near 8 drops?
That would depend on the contamination level of the water you were trying to purify...
City water straight out of the tap is over treated most places, so you can add NOTHING and have it last over a year in storage.
Water you want to last for more than Months, you should add about TWO drops of clear Chlorine (bleach) to for long term storage to inhibit microbial growth over time.
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If you are talking about trying to purify 'Raw' water that is clear, or 'Raw' water that is dark, you will have to use significantly more Chlorine to purify these than to preserve already 'Clean' water.
We need to know how 'Dark' the water is before anyone can even begin to recommend a level of treatment...