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Sodium hypochlorite is one form of chlorine used for water disinfection. It can be manufactured in most locations since it can be obtained through the electrolysis of salt water. Bottles can be purchased for household water treatment from many manufacturers in various sizes. Chlorine concentrations range from 0.5 to 10% and each product should have its own instructions for correct dosing of contaminated water. Liquid household bleach also contains sodium hypochlorite, and is widely available.
Chlorine forms hydrochloric acid when added to water which causes chemical reactions which deactivate contaminants and reacts through oxidization with micro-organisms, organic matter, manganese, iron and hydrogen sulphide.
'''Three things can happen when chlorine is added to water:'''
#Some chlorine reacts through oxidization with organic matter and the pathogens in the water and kills them. This portion is called consumed chlorine.
#Excess chlorine that is not consumed or combined remains in the water. This portion is called free residual chlorine (FRC). The FRC helps prevent recontamination of the treated water.
Chlorine began to be widely used as a disinfectant in the early 1900’s. It revolutionized drinking water treatment and dramatically reduced the incidence of waterborne diseases. Chlorine remains the most widely used chemical for water disinfection in the United States.
===Suitable conditions===
Unlimited amounts of water can be processed at a time, depending on the amount of active chlorine.
Some users complain about the taste and odour that chlorine may cause in water. Chlorine reacts with organic matter naturally present in water to form by-products such as trihalomethanes (THMs), which are potentially cancer-causing. Lantagne et al. (2008)<ref>[[#lantagne08|Lantagne et al. (2008)]]</ref> indicate that THM levels produced during household chlorination may fall below World Health Organization (WHO) guideline values. The use of household bleach products for household water treatment is not recommended in the absence of ongoing quality control testing, due to poor quality control of most sodium hypochlorite bleaches. If household bleach is used, the concentration should be regularly tested and an appropriate dosage strategy (2 mg/l for waters of turbidity 0-10 NTU, 4 mg/L for water of turbidity 10-100 NTU) should be developed by the recommending organization. {{procontable | proborder="1" cellpadding="5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Inexpensive <br>
- Kills bacteria nad viruses effectively <br>
- Residual chlorine protects water from recontamination <br>
- Plenty of testing and field assessments <br>
- Local familiarity with product <br>
| convalign= "top" | - Lower disinfection effectiveness in turbid waters contaminated with organic and some inorganic compounds <br>
- May not be effective at killing parasites <br>
- Taste and odor are unacceptable to some <br>
- Relatively short shelf life <br>
- Uncertain concentration and shelf life, susceptibility to gaps in supply chain, high transportation costs, and difficulty in dispensing precise quantities <br>
|}} ==History and social context==Chlorine began to be widely used as a disinfectant in the early 1900’s. It revolutionized drinking water treatment and dramatically reduced the incidence of waterborne diseases. Chlorine remains the most widely used chemical for water disinfection in the United States. ==Suitable conditions ==Unlimited amounts of water can be processed at a time, depending on the amount of active chlorine. Some users complain about the taste and odour that chlorine may cause in water. Chlorine reacts with organic matter naturally present in water to form by-products such as trihalomethanes (THMs), which are potentially cancer-causing. Lantagne et al. (2008)<ref>[[#lantagne08|Lantagne et al. (2008)]]</ref> indicate that THM levels produced during household chlorination may fall below World Health Organization (WHO) guideline values.
{{Potential_Treatment_Capacity_table
}}
==Technical specification=Construction, operations and maintenance===
There are several different brands of chlorine products that have been manufactured specifically for household water treatment. Each product should have its own instructions for correct dosing and contact time.
The contact time should be increased to 1 hour when the temperature is between 10˚ and 18˚C. It should be increased to two or more hours when the temperature falls below 10˚C.
<!--See CAWST’s Technical Brief on Chlorine Disinfection of Drinking Water for information on how to determine the chlorine dose and contact time using household bleach. -->
Metering pumps as [[Dosatron]] can be used for proportional dosing .
====Treatment Efficiency====
A recent meta-analysis showed that chlorine reduces the risk of child diarrhea by 29%
{| border="1" cellpadding="5" cellspacing="0" align="centernone"
|-
! style="background:#efefef;" |
| valign="top" | moderate<ref name=cdcp07/>
| valign="top" | high<ref name=cdcp07/>
| valign="top" | not availablehigh
|}
Toxoplasma oocysts and cryptosporidium oocysts are highly resistant to chlorine disinfection <ref name=cdcp07/>). Chlorine alone should not be expected to inactivate these pathogens in drinking water.
Chlorine should be stored in a cool, dark place in a closed container.
====Estimated Lifespan====
There are many producers of chlorine solutions all around the world. <!--See CAWST’s Sodium Hypochlorite Product Sheets for further details.-->
==Cost=Costs===
{{Treatment_Cost
|CapCost=US$ 0
Note: Program, transportation and education costs are not included.
==Country experiences=Field Experiences===The following project(s) utilize chlorine.<br>{|style="border: 2px solid #e0e0e0; width: 20%; text-align: justify; background-color: #e9f5fd;" cellpadding="2"|- style="vertical-align: top"|[[Image:akvorsr logo_lite.png|center|60px|link=http://akvo.org/products/rsr/]]|- style="vertical-align: bottom"|[[Image:project 810.png |thumb|center|140px|<font size="2"><center>[http://wash-liberia.akvoapp.org/en/project/810/ RSR Project 810]<br>Improved Water Sanitation and Hygiene</center></font>|link=http://wash-liberia.akvoapp.org/en/project/810/ ]] |}
==Movies=Manuals, videos, and links= ==External Links==* [http://fieldresearch.msf.org/msf/bitstream/10144/618835/1/FRC+Op+Guidance+Briefing+Note+%28Nov+2016%29.pdf Operational Guidance Briefing Note: Evidence-based Free Residual Chlorine (FRC) Targets]
*[http://www.cawst.org CAWST (Centre for Affordable Water and Sanitation Technology)]
*[http://www.enpho.org/drinking_water_quality.htm Drinking water quality information from Environment and Public Health Organization (ENPHO)]*[httphttps://www.cdc.gov/safewater/publications_pages/pubs_chlorinechlorination.htm html Centers for Disease Control and Prevention]
*[http://www.psi.org/child-survival Population Services International (PSI)]
*[[Solution_of_the_week_3|Akvo water solution of the week 3]]
==Footnotes=References===
<references/>
===Acknowledgements===
This article is based on a factsheet from [http://www.cawst.org/ Centre for Affordable Water and Sanitation Technology (CAWST)], which is gratefully acknowledged.
* <cite id=CDCP07>Centers for Disease Control and Prevention (CDC 2007). Effect of Chlorination on Inactivating Selected Pathogens. Available at:www.cdc.gov/safewater/about_pages/chlorinationtable.htm </cite>
* <cite id=Lantagne08>Lantagne, D.S., Blount, B. C., Cardinali, F., and R. Quick (2008). Disinfection by-product formation and mitigation strategies in point-of-use chlorination of turbid and non-turbid waters in western Kenya. Journal of Water and Health, 06.1, 2008.</cite>
* <cite id=luby01>Luby, S., Agboatwalla, M., Razz, A. and J. Sobel (2001). A Low-Cost Intervention for Cleaner Drinking Water in Karachi, Pakistan. International Journal of Infectious Diseases; 5(3): 144-150.</cite>Cambodia.</cite>
