Editing Chlorine (section)

==== Public sanitation ====
[[File:Mosul-swimming.jpg|thumb|Chlorinated water is used in [[swimming pools]] to disinfect water from microbial contaminants]]
[[File:Liquid Pool Chlorine.jpg|thumb|Liquid pool chlorine]]

The first continuous application of chlorination to drinking U.S. water was installed in [[Jersey City]], New Jersey, in 1908.<ref>Joseph Cotruvo, Victor Kimm, Arden Calvert. [http://www.epaalumni.org/hcp/drinkingwater.pdf "Drinking Water: A Half Century of Progress."] {{Webarchive|url=https://web.archive.org/web/20200731153608/http://www.epaalumni.org/hcp/drinkingwater.pdf |date=2020-07-31 }} EPA Alumni Association. March 1, 2016.</ref> By 1918, the [[US Department of Treasury]] called for all drinking water to be disinfected with chlorine. Chlorine is presently an important chemical for [[water purification]] (such as in water treatment plants), in [[disinfectant]]s, and in [[bleach]]. Even small water supplies are now routinely chlorinated.<ref name="CRC">{{cite book| author = Hammond, C. R.|title = The Elements, in Handbook of Chemistry and Physics|edition = 81st| publisher =CRC press| date = 2000| isbn = 978-0-8493-0481-1}}</ref>

Chlorine is usually used (in the form of [[hypochlorous acid]]) to kill [[bacteria]] and other microbes in [[drinking water]] supplies and public swimming pools. In most private swimming pools, chlorine itself is not used, but rather [[sodium hypochlorite]], formed from chlorine and [[sodium hydroxide]], or solid tablets of chlorinated isocyanurates. The drawback of using chlorine in swimming pools is that the chlorine reacts with the [[amino acid]]s in proteins in human hair and skin. Contrary to popular belief, the distinctive "chlorine aroma" associated with swimming pools is not the result of elemental chlorine itself, but of [[monochloramine|chloramine]], a chemical compound produced by the reaction of free dissolved chlorine with amines in organic substances including those in urine and sweat.<ref>{{cite web|title=Chloramines & Pool Operation|url=https://www.cdc.gov/healthywater/swimming/aquatics-professionals/chloramines.html|access-date=13 March 2022|publisher=Centres for Disease Control and Prevention|archive-date=13 March 2022|archive-url=https://web.archive.org/web/20220313130646/https://www.cdc.gov/healthywater/swimming/aquatics-professionals/chloramines.html|url-status=live}}</ref> As a disinfectant in water, chlorine is more than three times as effective against ''[[Escherichia coli]]'' as [[bromine]], and more than six times as effective as [[iodine]].<ref>{{cite journal|author=Koski T. A. |author2=Stuart L. S. |author3=Ortenzio L. F.|title=Comparison of chlorine, bromine, iodine as disinfectants for swimming pool water|journal = Applied Microbiology|volume = 14|issue = 2|date = 1966|pages = 276–79|pmid=4959984|pmc=546668|doi=10.1128/AEM.14.2.276-279.1966 }}</ref> Increasingly, [[monochloramine]] itself is being directly added to drinking water for purposes of disinfection, a process known as [[chloramination]].{{r|CDC-Chloramination}}

It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include [[hypochlorite]] solutions, which gradually release chlorine into the water, and compounds like [[sodium dichloro-s-triazinetrione]] (dihydrate or anhydrous), sometimes referred to as "dichlor", and [[trichloro-s-triazinetrione]], sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule, forming hypochlorous acid (HOCl), which acts as a general [[biocide]], killing germs, microorganisms, algae, and so on.{{sfn|Greenwood|Earnshaw|1997|p=860}}<ref>{{Holleman&Wiberg|page=411}}</ref>