Disinfection, one of the primary tools of water treatment, is the removal and inactivation of pathogenic microbes, that is, small organisms such as viruses, bacteria, and protozoa, that can cause disease. Disinfection has historically been accomplished using chlorination, the destruction of microbes by hypochlorous acid and the hypochlorous ion, formed by the reaction of chlorine gas and water or added directly as hypochlorite salts. Large improvements in public health occur when pathogen-free waters are available for human consumption, and significant portion of the life span increase achieved in the modern era is the result of safe drinking water.
However, there have been unintended consequences of disinfection by chlorination. If organic compounds are present in the water, halogenated disinfection by-products (DBPs) may be formed. Two halogenated DBPs regulated by U.S. drinking water standards are trihalomethanes (THM) and haloacetic acids. Both can increase the risk of cancer. THMs can also cause liver, kidney, and central nervous system problems. A USGS study found THMs in the drinking water of 45 percent of some 2,000 CWSs randomly selected in the Northeast and Mid-Atlantic regions of the United States. Fortunately, there are a number of ways CWSs can limit the generation of halogenated DBPs, including using water sources with low organic content, removing organic compounds before chlorination, and using disinfectants that produce fewer or no halogenated DBPs, such as ozone or chloramines. see also Abatement; Disinfection; Vehicular Pollution.
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