Alternatives
Chlorine in water is more than three times more effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and is more than six times more effective than an equivalent concentration of iodine.
Several alternatives to traditional chlorination exist, and have been put into practice to varying extents. Ozonation is used by many European countries and also in a few municipalities in the United States. Due to current regulations, systems employing ozonation in the United States still must maintain chlorine residuals comparable to systems without ozonation.
Disinfection with chloramine is also becoming increasingly common. Unlike chlorine, chloramine has a longer half life in the distribution system and still maintains effective protection against pathogens. The reason chloramines persist in the distribution is due to the relatively lower redox potential in comparison to free chlorine. Chloramine is formed by the addition of ammonia into drinking water to form mono-, di-, and trichloramines. Whereas Helicobacter pylori can be many times more resistant to chlorine than Escherichia coli, both organisms are about equally susceptible to the disinfecting effect of chloramine.
Water treated by filtration may not need further disinfection; a very high proportion of pathogens are removed by materials in the filter bed. Filtered water must be used soon after it is filtered, as the low amount of remaining microbes may proliferate over time.
The advantage of chlorine in comparison to ozone is that the residual persists in the water for an extended period of time. This feature allows the chlorine to travel through the water supply system, effectively controlling pathogenic backflow contamination. In a large system this may not be adequate, and so chlorine levels may be boosted at points in the distribution system, or chloramine may be used, which remains in the water for longer before reacting or dissipating.
Another method which is gaining popularity is UV disinfection. UV treatment leaves no residue in the water due to use of light instead of chemical disinfectants. However, this method alone (as well as chlorination alone) will not remove bacterially produced toxins, pesticides, heavy metals, etc. from water. Often, multiple steps are taken in commercially sold water.
Read more about this topic: Chlorination
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