Filtration is a purely mechanical, physical process for separating substances and/or particles from water. It ranges from the so-called pre-filtration, where e.g. contaminants such as sand, rust or protozoa >1 micrometer (larger than 0.001mm) are filtered, to the reverse osmosis process, where salts as well as single ions (atoms) <0.001 micrometer (smaller than 0.00001mm) are retained.

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