A Water Filter is a device which removes contaminants from water by means of a barrier, chemical process, or biological process. The basic functions of a water filter are to: remove chlorine and particulates, soften water for drinking and washing, and remove bad tastes and odors. Some filters will also remove bacteria, protozoa, and cysts.
Water filters are not to be confused with water purifiers which are held to higher EPA standards. Water purifiers also remove viruses such as Hepatitis A and rotavirus, etc. The scientific principles upon which water filtration works include sieving, adsorption, and ion exchanges. Adsorption is a process in which a gas or liquid solute (water) passes over a substance, such as activated charcoal, and certain chemicals and compounds in the solute attach or bond to the surface of the substance being used.
Activated charcoal is very good at bonding other carbon-based impurities. As it collects, it forms a thin atomic or molecular film. A major plus of activated charcoal filters is that it has a huge surface area in proportion to its size, allowing it to adsorb a lot of particulates and impurities. One of the drawbacks to using an activated charcoal filter is that it will completely ignore certain chemicals and compounds such as sodium and nitrates.