John Snow (1813–1858; not to be confused with the modern-day TV character Jon Snow) was a London physician. He helped to control a mass outbreak of cholera in the Soho district of the City of Westminster, London, England, in 1854. He deduced that the disease was being spread through the borough’s public wells. By administering doses of chlorine to the offending wells, he brought the epidemic to a standstill.
The addition of chlorine to public water supplies became commonplace in the beginning of the twentieth century, bringing about dramatic reductions in outbreaks of waterborne diseases such as typhoid and cholera. Chlorine is added to water supplies at the final step in the purification process, after flocculation, sedimentation, and filtration. Whilst some organisms, such as cryptosporidium, are resistant to it, chlorine remains the principal solution to water treatment globally.
An alternative to chlorine is chloramine. It is less volatile than chlorine, so exposure to the open air will not cause chloramine to evaporate as readily as chlorine will. Baristas wanting to avoid a flavour taint brought on by disinfection products will want to install an activated charcoal filter to their water mains (see Lesson 4.01).
This diagram shows you where disinfection occurs in the water treatment process. 1.) Reservoir 2.) Flocculation 3.) Sedimentation 4.) Filtration 5.) Disinfection — chlorine or chloramine 6.) Elevated storage — necessary to achieve mains pressure
Because some harmful microorganisms are resistant to chlorine, the ultraviolet (UV) system of disinfection was developed. This process briefly exposes water to UV radiation. It is as simple as piping water through a canister that has a UV light source flashing through it.