Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption (potable). Water which has been treated with chlorine is effective in preventing the spread of disease.
The chlorination of public drinking supplies was originally met with resistance, as people were concerned about the health effects of the practice. The use of chlorine has greatly reduced the prevalence of waterborne disease as it is effective against almost all bacteria and viruses. However, there are those who wish to move to other purification systems. They point to the production of dangerous by-products in the water when chlorine reacts with naturally occurring organic compounds found in the water supply. The most common of these are trihalomethanes (THMs), which include chloroform.
There are also other concerns regarding chlorine including its volatile nature which causes it to disappear too quickly from the water system, and aesthetic concerns such as taste.
Another method of purifying water is to use ozone. Some American municipalities (including Milwaukee, Wisconsin) have switched to that method, but ozone breaks down quickly so smaller amounts of chlorine are still added to these systems to ensure that water downstream from the treatment facility continues to be safe.
Purification with chloramine is also becoming increasingly common.
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