Most public utilities in the U.S. use some form of disinfection to protect consumers against the potential presence of bacteria in the drinking water supply. Chlorine, ozone, chloramines, and chlorine dioxide are some of the more common disinfection techniques used at water treatment facilities today. Unfortunately, over the years scientists have discovered that byproducts can form when these disinfectants react with natural organic matter, such as decaying vegetation, or when certain compounds, such as bromide, are present in the source water.
Although studies are being conducted to determine what potential health effects these byproducts may have if consumed by humans over long periods of time, the EPA has already set monitoring requirements and maximum contaminant levels for some of the more common byproducts, including trihalomethanes, haloacetic acids, bromate, and chlorite.
Chlorine is one of the most widely used forms of disinfection in the United States today. It is effective at killing many forms of pathogenic bacteria and viruses, although it is less effective at treating other microorganisms, such as parasites. Parasites or cysts, such as Cryptosporidium and Giardia, have a protective outer shell, which is difficult for chemical disinfectants such as chlorine to penetrate.
When chlorine is used to disinfect water supplies containing high levels of organic matter, water quality specialists have discovered that trihalomethanes (THMs) and haloacetic acids (HAAs) can form.
Ozone has been used for many years at bottled water production facilities and public water treatment facilities for purposes of disinfection. This type of disinfection super oxygenates the water, which kills many forms of bacteria and parasites. Because ozone does not leave a protective residual in the water, most water utilities combine the use of ozone with a form of chemical disinfection, such as chlorine, to help maintain the microbiological quality of the water as it leaves the plant and enters the distribution system.
Unfortunately, if bromide is present in the source water and ozone is used for disinfection, a chemical known as bromate can develop. The EPA has determined that bromate may pose a health risk, so they do require utilities using ozone to monitor for this compound. The amount permitted in public water supplies cannot exceed an annual average of 10 ppb.
Although chloramines have been used as a disinfectant in drinking water for many years, their use has not been widespread or highly publicized until recently. Because of concerns about the presence of high levels of chlorination byproducts, some communities have switched from chlorine to the use of chloramines for disinfection. Combining chlorine with ammonia creates chloramines. Although they are a weaker disinfectant than chlorine, chloramines are generally more stable, especially in the distribution system. In addition, they do not react as readily with organic matter in the treated water supplies, dramatically reducing the potential formation of disinfection byproducts, such as THMs and HAAs.
Although safe for human ingestion because chloramines are neutralized by our digestive systems, water that has been disinfected with chloramines should not be used directly in fish aquariums without first removing the chloramines with products specifically designed for that purpose. Chlorine can also be toxic to fish and should be removed before adding water to an aquarium.
Chlorine dioxide is another compound that can be used for disinfection purposes. As with the other disinfection processes mentioned above, byproducts may develop when using this compound. The EPA currently requires utilities using chlorine dioxide to monitor the water for chlorite. Federal regulations requires utilities to test at least three times a month for chlorite levels to ensure their monthly average does not exceed 1 part per million.
Thanks to the 1998 federal mandate requiring water utilities in the United States to prepare annual water quality reports, also known as Consumer Confidence Reports, it is possible for consumers to monitor and track the amount of disinfection byproducts present in their drinking water supplies. If you have any concerns about the presence of these compounds in your water, talk with your local water utility. The EPA's safe drinking water office also has further information available on the potential health risks associated with long-term exposure to these compounds.
Fortunately, several disinfection byproducts can be significantly reduced through the use of home water treatment devices. Consumers are welcome to contact the NSF Consumer Affairs Office toll-free at (1-800-673-8010 or via email at email@example.com, for further information about drinking water safety. In addition, detailed information about our drinking water treatment unit certification program, as well as a list of water treatment devices certified to reduce disinfection byproducts and other contaminants, is available online.
NSF International is a not-for-profit, non-governmental organization that provides product testing services and risk management solutions to the public.