<P> The practice of water treatment soon became mainstream and common, and the virtues of the system were made starkly apparent after the investigations of the physician John Snow during the 1854 Broad Street cholera outbreak . Snow was sceptical of the then - dominant miasma theory that stated that diseases were caused by noxious "bad airs". Although the germ theory of disease had not yet been developed, Snow's observations led him to discount the prevailing theory . His 1855 essay On the Mode of Communication of Cholera conclusively demonstrated the role of the water supply in spreading the cholera epidemic in Soho, with the use of a dot distribution map and statistical proof to illustrate the connection between the quality of the water source and cholera cases . His data convinced the local council to disable the water pump, which promptly ended the outbreak . </P> <P> The Metropolis Water Act introduced the regulation of the water supply companies in London, including minimum standards of water quality for the first time . The Act "made provision for securing the supply to the Metropolis of pure and wholesome water", and required that all water be "effectually filtered" from 31 December 1855 . This was followed up with legislation for the mandatory inspection of water quality, including comprehensive chemical analyses, in 1858 . This legislation set a worldwide precedent for similar state public health interventions across Europe . The Metropolitan Commission of Sewers was formed at the same time, water filtration was adopted throughout the country, and new water intakes on the Thames were established above Teddington Lock . Automatic pressure filters, where the water is forced under pressure through the filtration system, were innovated in 1899 in England . </P> <P> John Snow was the first to successfully use chlorine to disinfect the water supply in Soho that had helped spread the cholera outbreak . William Soper also used chlorinated lime to treat the sewage produced by typhoid patients in 1879 . </P> <P> In a paper published in 1894, Moritz Traube formally proposed the addition of chloride of lime (calcium hypochlorite) to water to render it "germ - free ." Two other investigators confirmed Traube's findings and published their papers in 1895 . Early attempts at implementing water chlorination at a water treatment plant were made in 1893 in Hamburg, Germany and in 1897 the city of Maidstone England was the first to have its entire water supply treated with chlorine . </P>

List of chemicals used in water treatment plants