Water Purification

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Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption (drinking water), but water purification may also be designed for a variety of other purposes, including meeting the requirements of medical, pharmacological, chemical and industrial applications. In general the methods used include physical processes such as filtration,sedimentation, and distillation, biological processes such as slow sand filters or biologically active carbon, chemical processes such asflocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light. The purification process of water may reduce the concentration of particulate matter including suspended particles, parasites, bacteria,algae, viruses, fungi; and a range of dissolved and particulate material derived from the surfaces that water may have made contact with after falling as rain. The standards for drinking water quality are typically set by governments or by international standards. These standards will typically set minimum and maximum concentrations of contaminants for the use that is to be made of the water. It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water – considered safe for all practical purposes in the 19th century – must now be tested before determining what kind of treatment, if any, is needed. Chemical and microbiological analysis, while expensive, are the only way to obtain the information necessary for deciding on the appropriate method of purification. According to a 2007 World Health Organization (WHO) report, 1.1 billion people lack access to an improved drinking water supply, 88 percent of the 4 billion annual cases of diarrheal disease are attributed to unsafe water and inadequate sanitation and hygiene, and 1.8 million people die from diarrheal diseases each year. The WHO estimates that 94 percent of these diarrheal cases are preventable through modifications to the environment, including access to safe water.[1] Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in safe containers could save a huge number of lives each year.[2] Reducing deaths from waterborne diseases is a major public health goal in developing countries.

Control room and schematics of the water purification plant to Lac de Bret, Switzerland. Contents  [hide]  * 1 Sources of water * 2 Treatment * 2.1 Pre-treatment * 2.1.1 pH adjustment * 2.2 Coagulation and flocculation * 2.3 Sedimentation * 2.3.1 Sludge storage and removal * 2.3.2 Floc blanket clarifiers * 2.4 Dissolved air flotation * 2.5 Filtration * 2.5.1 Rapid sand filters * 2.5.2 Slow sand filters * 2.6 Membrane filtration * 2.7 Removal of ions and other dissolved substances * 2.8 Disinfection * 2.8.1 Chlorine disinfection * 2.8.2 Chlorine dioxide disinfection * 2.8.3 Chloramine disinfection * 2.8.4 Ozone disinfection * 2.8.5 Ultraviolet disinfection * 2.8.6 Various portable methods of disinfection * 2.8.7 Solar water disinfection * 2.9 Additional treatment options * 3 Other water purification techniques * 4 Safety and controversies * 4.1 Demineralized water * 5 See also * 6 References * 7 Further reading * 8 External links| -------------------------------------------------

[edit]Sources of water
Further information: Water supply
1. Groundwater: The water emerging from some deep ground water may have fallen as rain many tens,...
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