The sole purpose of this page is to provide referral links to a scientific document about slow sand filtration published by the WHO in 1974. The document can be accessed on who.int, the official website of the World Health Organization.
Slow sand filtration, also called ‘biological filtration’, is an old (first documented use in Scotland, 1804) and inexpensive method to filter water that can be used under a range of different circumstances. The level of water purity that the method provides cannot be compared to the level anticipated from let’s say reverse osmosis filtration or water distillation. However, if your feed water is already relatively clean, slow sand filtration can be sufficient to produce drinking water safe for human consumption.
The biggest advantage of slow sand filtration is its cost-efficiency, which is the reason why to this day it still gets applied even in developed countries. Also, it does not require pressure, chemicals, or electricity and only minimal operator training and periodic maintenance. Therefore it’s often used in poor regions around the world.
As filtration takes a long time and a vast area is needed, throughout the years many slow sand filters have been replaced by rapid sand filters as cities have started to grow and the demand for drinking water has increased.
If you are interested to learn more about the method, e.g. about the construction and operation of modern slow sand filters or the theory of biological filtration, take a look at the publication linked below. The document was first published in 1974, but remains to be valid until this day as there is still a demand for it. It is made available by the WHO in electronic form.
Prepared by L. Huismans and W.E. Wood
ISBN 92 4 154 037 0
© World Health Organization 1974
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