A water filter removes impurities from water by means of a fine physical barrier, a chemical process or a biological process. Filters cleanse water to different extents for purposes like irrigation, drinking water, aquariums, and swimming pools.
During the 19th and 20th centuries, water filters for domestic water production were generally divided into slow sand filters and rapid sand filters, also called mechanical filters and American filters. While there were many small-scale water filtration systems prior to 1800, Paisley, Scotland is generally acknowledged as the first city to receive filtered water for an entire town. The Paisley filter began operation in 1804 and was an early type of slow sand filter. Throughout the 1800s, hundreds of slow sand filters were constructed in the UK and on the European continent. An intermittent slow sand filter was constructed and operated at Lawrence, Massachusetts in 1893 due to continuing typhoid fever epidemics caused by sewage contamination of the water supply.The first continuously operating slow sand filter was designed by Allen Hazen for the city of Albany, New York in 1897.The most comprehensive history of water filtration was published by Moses N. Baker in 1948 and reprinted in 1981.
In the 1800s, mechanical filtration was an industrial process that depended on the addition of aluminum sulfate prior to the filtration process. The filtration rate for mechanical filtration was typically more than 60 times faster than slow sand filters, thus requiring significantly less land area. The first modern mechanical filtration plant in the U.S.
was built at Little Falls, New Jersey for the East Jersey Water Company. George W. Fuller designed and supervised the construction of the plant which went into operation in 1902.In 1924, John R. Baylis developed a fixed grid backwash assist system which consisted of pipes with nozzles that injected jets of water into the filter material during expansion.
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), microfiltration 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.
Point-of-use microfiltration devices can be directly installed at water outlets such as faucets and shower in order to protect users against Legionella spp., Pseudomonas spp., Nontuberculousmycobacteria, Escherichia coli and other potentially harmful water pathogens by providing a barrier to them and/or minimizing patient exposure.
Water filters are used by hikers, aid organizations during humanitarian emergencies, and the military. These filters are usually small, portable and lightweight (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.
While water is essential for life it is important to be certain it is safe to drink. There are many areas where tap water is quite fine, but it is better to be safe than sorry.