Water filters - why sand and rocks?
Saw a video on youtube where some guy made a water filter out of a bottle, charcoal, sand and little rocks. He commented that since the charcoal is very porous it's great for filtering. Then, after constructing the filter he continued to filter some dirty water and commented that the first little bit is going to be nasty since its getting the dirt off the sand and rocks in the filter.
This doesn't make sense to me, if the charcoal is so great, and all that the rocks and sand bring to the party is dirt, why not just fill the bottle with all charcoal? Not to mention that charcoal is much easier to come by than various grains of sand in a forest or a jungle or whatever.
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His filter has basically two stages:
- A series of mechanical filters (coarse rocks, fine rocks, coarse sand, fine sand) to remove macroscopic contaminants (eg. dirt) from the water. By using several different sizes of material, he's extending the life of the filter: each layer will tend to block material that would clog the next layer down, with the fine sand acting to protect the charcoal.
- A chemical filter (charcoal) to remove chemical contaminants from the water. This doesn't work by physically blocking them, but by absorption: essentially, the chemicals "stick" to the charcoal as the water moves past it.
It's important to note that this will not deal with microbes. Some protozoa will be stopped by the fine sand, and some viruses will stick to the charcoal, but most will get through. If you want to be safe, you need to use this in combination with boiling or another method of dealing with microbial contamination.
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Any little bit a person can do that can increase their chances of staying healthy is not only important, but potential lifesaving.
I have lived in the bush and was in the military and in an emergency situation, you definitely want to think about water cleanliness. No, you may not be able to guarantee you will not get sick, but getting lost in the bush plus intestinal issues equal dehydration, which is, without a doubt, one of the most dangerous positions one can find themselves in when in a survival situation.
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According to wildwoodsurvival, the sand helps remove suspended particles. Charcoal helps to remove chemical impurities. The charcoal plays the role of active carbon.
The water filtration process use multiple materials, from coarse to fine, to prevent clogging. As a last stage, the charcoal can also help remove some bacterias.
Note that the author of the video recommendeds this method solely for water filtration and not water purification.
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