Water chlorination

[[File:Fort Smith Municipal Water Plant 10.jpg|thumb|right|165px|Chlorine system at a municipal water treatment plant]]
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'''Water chlorination''' is one of several, and the oldest, method of sterilizing water. Commercially viable methods of disinfecting water include chlorination (Cl<sub>2</sub>), chloramination (NH<sub>2</sub>Cl), and [[Ozone|ozonation]] (O<sub>3</sub>). Other less cost-effective methods of disinfection are ultraviolet light and reverse osmosis filtration. Prior to disinfection, naturally-sourced groundwater typically contains a microbiome that can contain harmful [[bacteria]]. After treatment, if insufficient disinfecting chemicals are not carried through the water system to consumers, harmful microbes can reenter the water.

==History==
The earliest methods of drinking water treatment date back to 4000 BCE, using filtration, boiling and sunlight. These methods primarily focused on aesthetics: taste and clarity. In 1855, John Snow proved that cholera was a waterborne disease, linking it to sewage contamination of water supplies. Reducing turbidity (i.e., dissolved solids) of drinking water by filtration reduced bacterial contamination somewhat, but it was chemical disinfection that was most effective. Water chlorination began in the [[United States]] in the mid- to late-19<sup>th</sup> century but did not become widespread until the early 20<sup>th</sup> century. In 1914, the U.S. Public Health Service set drinking water standards for bacterial content.<ref name="usepa">[http://www.epa.gov/ogwdw/consumer/pdf/hist.pdf US Environmental Protection Agency: The History of Drinking Water Treatment] (2000). EPA-816-F-00-006.</ref>

==Safety==
A study showing the effects of increasing doses of chlorine in humans showed no adverse effects at any of the doses studied.<ref>[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1569027/ Controlled clinical evaluations of chlorine dioxide, chlorite and chlorate in man] by J. R. Lubbers et al. ''Environ. Health Perspect.'' 1982 Dec; 46: 57–62.</ref> Drinking water chlorination is rather safe, even in cases of relatively heavy water chlorination. Water that has not been sanitized is much more dangerous than chlorinated water.<ref>[http://www.who.int/water_sanitation_health/diseases-risks/diseases/cyanobacteria/en/ Water sanitation hygiene: Water-related diseases, Cyanobacterial Toxins] World Health Organization</ref>

==Benefits==
Typhoid, cholera, and dysentery can be carried through water systems unless the water is disinfected. The widespread disinfection of water is one of the greatest life-saving achievements in history.<ref name="usepa"/>

==Risks==
The methods of water disinfection that use chlorinated chemicals create low concentrations of [[Cancer|carcinogenic]] chemicals from the reaction of chlorine with humic acids.<ref>[http://www.ncbi.nlm.nih.gov/pubmed/16291527 Carcinogenicity of the chlorination disinfection by-product MX] by McDonald TA & Komulainen H. ''J. Environ. Sci. Health C Environ. Carcinog. Ecotoxicol. Rev.'' 2005;23(2):163-214.</ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/2880712 Carcinogenicity of by-products of disinfection in mouse and rat liver] by Herren-Freund SL & Pereira MA ''Environ. Health Perspect.'' 1986 Nov;69:59-65.</ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/17980649 Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research] by Richardson SD et al. ''Mutat. Res.'' 2007 Nov-Dec;636(1-3):178-242. Epub 2007 Sep 12.</ref> Recently water treatment facilities have been phasing out chlorination in favor of other disinfection methods, at least in part to reduce the potential carcinogenicity of treated water. Unfortunately, most alternatives are more expensive.<ref>[http://www.ajol.info/index.php/wsa/article/download/5161/12701 Chlorine: Is it really so bad and what are the alternatives?] by S. D. Freese & D. J. Nozaic (2004). ''Water SA'' Vol. 30 No. 5 (Special edition).</ref>

==See also==
*[[Water fluoridation]]

==References==
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