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A water filter removes impurities by lowering contamination of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents, for purposes such as: providing agricultural
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
, accessible
drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...
, public and private
aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...
s, and the safe use of ponds and
swimming pool A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...
s.


Methods of filtration

Filters use
sieving A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. ...
,
adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
,
ion exchange Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
s,
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
s and other processes to remove unwanted substances from water. Unlike a
sieve A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. T ...
or
screen Screen or Screens may refer to: Arts * Screen printing (also called ''silkscreening''), a method of printing * Big screen, a nickname associated with the motion picture industry * Split screen (filmmaking), a film composition paradigm in which mul ...
, a filter can potentially remove particles much smaller than the holes through which its water passes, such as Nitrates or germs like ''
Cryptosporidium ''Cryptosporidium'', sometimes informally called crypto, is a genus of apicomplexan parasitic alveolates that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea (intestinal cryptosp ...
.'' Among the methods of filtration, notable examples are
sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...
, used to separate hard and suspended solids from water and
activated charcoal "Activated" is a song by English singer Cher Lloyd. It was released on 22 July 2016 through Vixen Records. The song was made available to stream exclusively on ''Rolling Stone'' a day before to release (on 21 July 2016). Background In an interv ...
treatment, where the boiled water is poured through a piece of cloth to trap undesired residuals. Additionally, the use of machinery to work on desalinization and purification of water through the transposal of it into multiple-filtration
water tanks A water tank is a container for storing water. Water tanks are used to provide storage of water for use in many applications, drinking water, irrigation agriculture, fire suppression, agricultural farming, both for plants and livestock, chemic ...
. This technique is aimed at the filtration of water on bigger scales, such as serving entire cities. These three methods are particularly relevant, as they trace back to centuries and are the base for many of the modern methods of filtration utilized today.


Types


Water treatment plant filters

Types of water filters include
media filter A media filter is a type of filter that uses a bed of sand, peat, shredded tires, foam, crushed glass, geo-textile fabric, anthracite, crushed granite or other material to filter water for drinking, swimming pools, aquaculture, irrigation, storm ...
s,
screen filter A screen filter is a type of iltration of waterusing a rigid or flexible screen to separate sand and other fine particles out of water for irrigation or industrial applications. These are generally not recommended for filtering out organic matte ...
s,
disk filter A disc filter is a type of water filter used primarily in irrigation, similar to a screen filter, except that the filter cartridge is made of a number of plastic discs stacked on top of each other like a pile of poker chips. Each disc is cover ...
s, slow sand filter beds,
rapid sand filter The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal drinking water facilities as part of a multiple-stage treatment system. Rapid sand filters were first developed in the ...
s,
cloth filter A cloth filter is a simple and cost-effective appropriate technology method for reducing the contamination of drinking water, developed for use mainly in Bangladesh. Water collected in this way has a greatly reduced pathogen count. Though not a ...
s, and biological filters such as
algae scrubber An algae scrubber is a water filtering device (not to be confused with a scrubber pad used to clean glass) which uses light to grow algae; in this process, undesirable chemicals are removed from the water. Algae scrubbers allow saltwater, fr ...
s.


Point-of-use filters

Point-of-use filters for home use include granular-activated carbon filters (GAC) used for
carbon filtering Carbon filtering is a method of filtering that uses a bed of activated carbon to remove impurities from a fluid using adsorption. Mechanism Carbon filtering works by adsorption, in which pollutants in the fluid to be treated are trapped inside the ...
,
depth filter Depth filters are the variety of filters that use a porous filtration medium to retain particles throughout the medium, rather than just on the surface of the medium. These filters are commonly used when the fluid to be filtered contains a high l ...
, metallic alloy filters, microporous ceramic filters, carbon block
resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...
(CBR),
microfiltration Microfiltration is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane filter to separate microorganisms and suspended particles from process liquid. It is commonly used in conjunction ...
and
ultrafiltration Ultrafiltration (UF) is a variety of membrane filtration in which forces such as pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the ...
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
kettle A kettle, sometimes called a tea kettle or teakettle, is a type of pot specialized for boiling water, commonly with a ''lid'', ''spout'', and ''handle'', or a small electric kitchen appliance of similar shape that functions in a self-contained ...
s have built-in filters, primarily to reduce
limescale Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of old ...
build-up. Standard Flowmatic cartridge style filters are added to existing plumbing; the filter cartridges are cylinders long by in diameter. They are made by multiple manufactures and are available in 0.5-100 micron ratings as well as activated carbon. Some common substances that filtration does not remove are arsenic, bacteria, chlorides, fluoride, nitrates, perechlorates, pharmaceuticals, sodium and viruses.


Portable water filters

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). These usually filter water by working a mechanical hand pump, although some use a
siphon A siphon (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in a ...
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 Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
,
protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
and
microbial cyst A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist or rarely an invertebrate animal, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of ...
s that can cause disease. Filters may have fine meshes that must be replaced or cleaned, and
ceramic water filter Ceramic water filters (CWF) are an inexpensive and effective type of water filter that rely on the small pore size of ceramic material to filter dirt, debris, and bacteria out of water. This makes them ideal for use in developing countries, and po ...
s must have its outside abraded when they have become clogged with impurities. These water filters should not be confused with devices or tablets that disinfect water which remove or kill
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...
es such as
hepatitis A Hepatitis A is an infectious disease of the liver caused by ''Hepatovirus A'' (HAV); it is a type of viral hepatitis. Many cases have few or no symptoms, especially in the young. The time between infection and symptoms, in those who develop them ...
and
rotavirus ''Rotavirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae''. Rotaviruses are the most common cause of diarrhoeal disease among infants and young children. Nearly every child in the world is infected with a rotavirus a ...
.


Ceramic water filters

Ceramic filters represent low-cost solutions to water filtration and are widely adhered to despite being one of the oldest methods of filtration. These filters are found not only inside the homes of families but also utilized in industrial engineering (as high-temperature filters) for several processes. The conventional ceramic filters used for day-to-day water consumption, known as candle-type filters, work with
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
and a central candle, which makes the filtration process significantly long.


Certification in the United States

Three organizations are accredited by the
American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
, and each one of them certified products using American National Standard Institute/National Science Foundation standards. Each American National Standards Institute/National Science Foundation standard requires verification of contaminant reduction performance claims, an evaluation of the unit, including its materials and structural integrity, and a review of the product labels and sales literature. Each certifies that home water treatment units meet or exceed National Standard Institute/National Science Foundation and
Environmental Protection Agency A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...
drinking water standards. American National Standard Institute/National Science Foundation standards are issued in two different sets, one for health concerns (such as removal of specific contaminants (Standard 53, Health Effects) and one for aesthetic concerns (Aesthetic Effects, such as improving taste or appearance of water). Certification from these organizations will specify one or both of these specific standards.


NSF International

NSF International as it is now known started out as the National Sanitation Foundation in 1944 at the University of Michigan School of Public Health. The NSF's water treatment Device Certification Program requires extensive product testing and unannounced audits of production facilities. One goal of this not for profit organization is to provide assurance to consumers that the water treatment devices they are purchasing meet the design, material, and performance requirements of national standards.


Underwriters Laboratories

Underwriters Laboratories The UL enterprise is a global safety science company headquartered in Northbrook, Illinois, composed of three organizations, UL Research Institutes, UL Standards & Engagement and UL Solutions. Established in 1894, the UL enterprise was founded a ...
, Inc., is an independent, accredited testing and certification organization that certifies home water treatment units which meet or exceed EPA and American National Standard Institute/National Science Foundation drinking water standards of contaminant reduction, aesthetic concerns, structural integrity, and materials safety.


Water Quality Association

The Water Quality Association is a trade organization that tests water treatment equipment, and awards its Gold Seal to systems that meet or exceed ANSI/NSF standards for contaminant reduction performance, structural integrity, and materials safety. Filters that use
reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
, those labeled as “absolute one micron filters,” or those labeled as certified by an American National Standards Institute (ANSI)- accredited organization to American National Standard Institute/National Science Foundation Standard 53 for “Cyst Removal” provide the greatest assurance of removing
Cryptosporidium ''Cryptosporidium'', sometimes informally called crypto, is a genus of apicomplexan parasitic alveolates that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea (intestinal cryptosp ...
. As with all filters, follow the manufacturer’s instructions for filter use and replacement.


Water polishing

The term water polishing can refer to any process that removes small (usually microscopic) particulate material, or removes very low concentrations of dissolved material from water. The process and its meaning vary from setting to setting: a manufacturer of
aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...
filters may claim that its filters perform water polishing by capturing "micro particles" within
nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from petro ...
or
polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
pads 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. In this sense, water polishing is simply another term for whole house water filtration systems. Polishing is also done on a large scale in water reclamation plants.


History

4000 years ago, in India and China,
Hindus Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
devised the first drinking water standards. Hindus heated dirty water by boiling it and exposing it to sunlight or dipping it seven times in hot pieces of copper, then filtering it through earthen vessels and cooling it. This was an enlightened procedure to obtain sterilized drinking water as well as to keep it aesthetically pleasing. This method was directed at individuals and households rather than for use as a community water source. The Egyptians first discovered the principle of coagulation in water treatment after 1500 BC. They adapted a chemical called alum for the settling of suspended particles. Until the invention of the microscope, the existence of microscopic life was undiscovered. More than 200 years passed before the microscope was invented and the relationship between microorganisms and disease became clear. in the mid-19th century, cholera was proven to be transmitted by contaminated water. in the late 19th century, Louis Pasteur's theory of the particulate pathogen finally established a causal relationship between microorganisms and disease. Filtration as a method of water purification was established in the 18th century, and the first municipal water treatment plant was built in Scotland in 1832. However, the aesthetic value of water was important at the time, and effective water quality standards did not exist until the late 19th century. 2,000 years ago,
Mayan Mayan most commonly refers to: * Maya peoples, various indigenous peoples of Mesoamerica and northern Central America * Maya civilization, pre-Columbian culture of Mesoamerica and northern Central America * Mayan languages, language family spoken ...
drinking water filtration systems used crystalline
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
and
zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These pos ...
. Both minerals are used in modern water filtration. "The filters would have removed harmful microbes, nitrogen-rich compounds, heavy metals such as mercury and other toxins from the water". Persian engineer
Al-Karaji ( fa, ابو بکر محمد بن الحسن الکرجی; c. 953 – c. 1029) was a 10th-century Persian people, Persian mathematician and engineer who flourished at Baghdad. He was born in Karaj, a city near Tehran. His three principal sur ...
(c. 953–1029) wrote a book, ''The Extraction of Hidden Waters'', which gave an early description of a water filtration process. During the 19th and 20th centuries, water filters for domestic water production were generally divided into
slow sand filters Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water. The length and bre ...
and
rapid sand filter The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal drinking water facilities as part of a multiple-stage treatment system. Rapid sand filters were first developed in the ...
s (also called mechanical filters and American filters). While there were many small-scale water filtration systems prior to 1800,
Paisley, Scotland Paisley ( ; sco, Paisley, gd, Pàislig ) is a large town situated in the west central Lowlands of Scotland. Located north of the Gleniffer Braes, the town borders the city of Glasgow to the east, and straddles the banks of the White Cart Wate ...
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 Lawrence is a city located in Essex County, Massachusetts, United States, on the Merrimack River. At the 2020 census, the city had a population of 89,143. Surrounding communities include Methuen to the north, Andover to the southwest, and Nort ...
in 1893 due to continuing typhoid fever epidemics caused by sewage contamination of the water supply.Baker, Moses N. (1981). ''The Quest for Pure Water: the History of Water Purification from the Earliest Records to the Twentieth Century.'' 2nd Edition. Vol. 1. Denver: American Water Works Association, 64-80. The first continuously operating slow sand filter was designed by
Allen Hazen Allen Hazen (August 28, 1869 – July 26, 1930) was an expert in hydraulics, flood control, water purification and sewage treatment. His career extended from 1888 to 1930 and he is, perhaps, best known for his contributions to hydraulics with the ...
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
aluminium sulfate Aluminium sulfate is a salt with the chemical formula, formula aluminium, Al2sulfate, (SO4)3. It is soluble in water and is mainly used as a Coagulation (water treatment), coagulating agent (promoting particle collision by neutralizing charge) in ...
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 George Warren Fuller (December 21, 1868 – June 15, 1934) was an American sanitary engineer who was also trained in bacteriology and chemistry. His career extended from 1890 to 1934 and he was responsible for important innovations in water and ...
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.Baylis, John R. (1959). "Review of Filter Bed Design and Methods of Washing." ''Journal AWWA.'' 51:11 1433-54.


See also

*
Backwashing (water treatment) In terms of water treatment, including water purification and sewage treatment, backwashing refers to pumping water backwards through the filters media, sometimes including intermittent use of compressed air during the process. Backwashing is ...
*
Carbon filtering Carbon filtering is a method of filtering that uses a bed of activated carbon to remove impurities from a fluid using adsorption. Mechanism Carbon filtering works by adsorption, in which pollutants in the fluid to be treated are trapped inside the ...
*
Distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...
*
Reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
* Reverse osmosis plant * Sand separator *
Settling basin A settling basin, settling pond or decant pond is an earthen or concrete structure using sedimentation to remove settleable matter and turbidity from wastewater. The basins are used to control water pollution in diverse industries such as agricul ...
* Swimming pool sanitation *
Water softening Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also exten ...
* Kinetic Degradation Fluxion Media


References


External links

* {{DEFAULTSORT:Water Filter Water filters Irrigation Hiking equipment Water conservation