Water under high pressure is forced through a membrane, a thin material with
very small pores, stopping small particles (including bacteria).
Source: GreenFacts
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There are four categories of membrane filtration: reverse osmosis (RO),
nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). As opposed
to granular activated carbon, membrane filtration is a non-absorbent water
treatment method.
