Filter (water)

  A water filter is a device which removes impurities from water by means of a fine physical barrier, chemical process and/or biological process. Filters are used to cleanse water for irrigation, drinking water, aquariums, and swimming pools.

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Uses

Water filters are primarily used to soften water and remove chemicals such as chlorine. This can be for health reasons in the case of harmful substances, or aesthetic reasons, to remove a disagreeable taste or smell.

Emergency drinking water

Water filters are also used by recreational hikers, by aid organizations during humanitarian emergencies, and by the military. These filters are usually small, portable and light (1-2 pounds or less) and usually filter water by working a mechanical hand pump, although some use a siphon drip system to force water through. Dirty water is pumped via a screen-filtered flexible silicon tube through a specialized filter, ending up in a container. These types of filters work to remove bacteria, protozoa and microbial cysts, all of which can cause disease. Filters include fine meshes, which must be replaced, and ceramic filters which must have their outside abraded off when it becomes clogged with impurities.

These water filters should not be confused with devices or tablets that are water purifiers. Water purifiers satisfy higher EPA standards, and also remove or kill viruses such as hepatitis A and rotavirus. In a domestic emergency, where water needs will last beyond those of stored, bottled water, a device that is specifically certified as a water purifier, and not a water filter, is preferred.

Methods of filtration

Main article: Filtration

The physics of filters is based on sieving, adsorption, ion exchanges and other processes. Unlike a sieve or screen, a filter can remove particles much smaller than the holes through which the water passes.

Types of filters

Types of filters include media filters, screen filters, disk filters, slow sand filter beds, rapid sand filters and cloth filters.

See also

• Backwash (physical phenomenon)
• Water purification
• Reverse osmosis
• Distillation
• Sand separator
• Settling basin
• Swimming pool sanitation