How does water get filtered while passing through sand, charcoal, etc.?
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The idea behind water filtration is that water particles are smaller than whatever contaminants are present in it, and we filter it through a series of smaller sieves to trap and separate the contaminants.
Let’s take some muddy water taken from a pond with sticks and leaves, for example:
With your hands, you should be capable of removing large contaminants, like sticks and medium to small sized leaves, but you won’t be able to remove the mud or small leaves and other contaminants, so you use a slightly finer sieve. A layer of gravel would be capable of trapping some mud, larger leaves, bugs and whatever you missed with your hands, but won’t get rid of all the mud or bacteria, so you use a slightly finer sieve. Coarse sand might be able to trap the majority of the mud, but it would not be able to trap other smaller impurities, so you use a finer sieve. Activated charcoal might remove contaminants with affinity to charcoal, but won’t remove bacteria or smaller contaminants, so you use a finer sieve. Fine sand might remove most of the contaminants, but it won’t remove all of the bacteria or contaminants that might go through that sieve. At this point, you could use a finer sieve, but we would be seeing diminishing returns. To kill the bacteria, you can treat it with chlorine, uv radiation, or in a pinch boiling, but this does not guarantee that water is safe to drink because you don’t know what other contaminants are in the water. Finally, you can distill the water to separate it from whatever contaminants are left over.
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