I really do need to look into the magic that is activated carbon filtration, but I do know it has something to do with the incredible amount of surface area that activated carbon has. Regardless of whether I actually know the science behind it, there is a great link (in not-so-great English) on how to build your own charcoal water filter from just about nothing.
I’ll paraphrase here:
There is a picture at the site that further explains what proportions to use.
The key is that the charcoal you’ll use will come straight from your very own campfire. That’s right, just go through the remnants of your fire (watch out for hot coals!) and pick out the black nuggets that are the charcoal. For such a potentially life-saving device, it’s incredibly easy to make.
I saw demonstrated on television a method of extracting water from the ground using nothing more than a container and a sheet of clear plastic. It does not produce a large quantity of water, but some is better than none. What this method does is essentially distill water out of the soil.
Solar energy will turn this setup into a miniature greenhouse and solar distillery. Water in the soil will evaporate and condense on the inner surface of the plastic sheet. When enough condensate accumulates, drops will form, which will then run down the slight slope produced by the weight on top of the sheet, and then drop into your open-top container.
To get the water collected, you’ll need to take the plastic up, which will let all the hot, moist air out of your makeshift solar still. So it is best to leave it as long as possible to collect the most water you can. Perhaps building it early in the morning and collecting at twilight or late evening would be best. If you are in a desperate state of thirst, you can always use a small-diameter tube as a straw, placing one end in your container and routing it out of the hole under the plastic sheet.
The amount of water collected will depend on soil conditions. However, it may be possible to use this method to distill murky or contaminated water by pouring the unpotable water into the hole before covering it with the plastic.
Larger holes, and multiple holes, may be dug, limited only by the amout of clear plastic sheeting you have. Translucent sheeting should also work. Opaque sheeting may work, but likely not as quickly as most of the solar energy will be turned into heat in the sheet, instead of passing through into the soil.
If you wanted to get extreme in your water conservation, you could dig a hole big enough to live in, cover it with plastic, and live in the hole with your open container. The moisture in your breath would eventually be collected, as would water expelled in your urine and feces. Of course, you’d be living in a warm, humid hole with urine, feces, a cup of water, and no ventillation, so I wouldn’t recommend this. {wink}