Types of filters

Water treatment plant filters

Main article: Water purification

Types of water filters include media filters, screen filters, disk filters, slow sand filter beds, rapid sand filters and cloth filters.^[1]

[edit] Point-of-use filters

Point-of-use filters for home use include granular activated carbon filters (GAC) used for carbon filtering, metallic alloy filters, microporous ceramic filters, carbon block resin (CBR) and ultrafiltration membranes. Some filters use more than one filtration method. An example of this is a multi-barrier system. Jug filters can be used for small quantities of drinking water. Some kettles have built-in filters, primarily to reduce limescale buildup.

[edit] Portable water filters

Main article: Portable water purification

Water filters are used by hikers, by aid organizations during humanitarian emergencies, and by the military. These filters are usually small, portable and light (1-2 pounds/0.5-1.0 kg or less), and usually filter water by working a mechanical hand pump, although some use a siphon drip system to force water through while others are built into water bottles. Dirty water is pumped via a screen-filtered flexible silicon tube through a specialized filter, ending up in a container. These filters work to remove bacteria, protozoa and microbial cysts that can cause disease. Filters may have fine meshes that must be replaced or cleaned, and ceramic water filters must have their outside abraded when they have become clogged with impurities.

These water filters should not be confused with devices or tablets that are water purifiers, some of which remove or kill viruses such as hepatitis A and rotavirus.

[edit] Homemade water filters

A homemade waterfilter for making drinking water

Water filters can be made on-site using local materials such as grass, charcoal (e.g. from burned firewood), and sand. These filters have been used by soldiers and outdoor enthusiasts.^[2] Due to their low cost they can be made and used by anyone, including the poor, who often do not have access to safe drinking water. Regrettably such filters do little if anything to mitigate against pathogens and other harmful constituents and can give a false sense of security that the water so produced is potable.

[edit] Water polishing

The term water polishing can refer to any process that removes small (usually microscopic) unwanted material from a portion of water. The process and its meaning vary from setting to setting: a manufacturer of aquarium filters may claim that its filters perform water polishing by capturing "micro particles" within nylon or polyester pads^[3] just as a chemical engineer can use the term to refer to the removal of magnetic resins from a solution by passing the solution over a bed of magnetic particulate.^[4] In this sense, water polishing is simply another term for water filtration.