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Water utilities play a central role in protecting public health by ridding drinking water of potentially harmful bacteria, viruses and other microorganisms. They do so through a treatment process called disinfection.

While disinfection is responsible for preventing many water-borne illnesses, there are concerns about disinfection byproducts (DBPs). DBPs form when chemical disinfectants, like chlorine, react with naturally occurring compounds in the water.

All commonly used chemical disinfectants form DBPs. The U.S. Environmental Protection Agency regulates five kinds of DBPs at levels that current research considers safe. Click below to learn more about DBPs.


Animal research has shown that exposure to high concentrations of DBPs can increase the risk of cancer. There is particular concern about bladder cancer. However, these studies were conducted using DBP concentrations that are much higher than those found in drinking water.

Over the past several years, a handful of studies have also shown a possible link between high levels of DBPs in tap water and adverse effects on reproductive health, including low birth weight and miscarriage. Other studies have failed to demonstrate such a linkage. Experts agree that the research on DBPs and health effects is preliminary and inconclusive, so research is ongoing.

Utilities are working to achieve DBP reductions. Since 1984, American drinking water utilities have spent almost $23 million researching DBP occurrence, health effects and treatment.

Disinfection of drinking water is vital to protecting the public against disease. Chlorine has been used to treat North American water supplies for most of the last century and is still the most widely used disinfectant. The use of chlorine and other disinfectants has virtually eliminated instances of waterborne diseases like typhoid fever, cholera and dysentery in the United States and other developed countries.

It is widely acknowledged that filtration and disinfection of drinking water have played a large role in the 20th century’s 50 percent increase in life expectancy. Both the World Health Organization and the U.S. Centers for Disease Control and Prevention describe water filtration and disinfection as among the most significant advancements of the last century.

In treating drinking water, utilities typically disinfect water twice. During primary disinfection, their goal is to kill or inactivate microorganisms present in water arriving from a source, such as a lake or river. At this stage, utilities can use chlorine-based disinfectants as well as techniques such as ozonation or UV disinfection.

Ozonation uses ozone—a molecule containing three oxygen atoms—to kill microbes.

UV disinfection relies on the power of ultra violet light, the kind that is responsible for sunburns! UV rays can also inactivate or kill microorganisms.

However, these forms of disinfection do not remain in the water long enough to offer protection as the water travels through the distribution system and into consumer’s homes. Secondary treatment is designed to prevent organisms from re-growing as the water travels from the treatment plant, through the distribution system pipes, all the way to consumers' homes. Only chlorine-based disinfectants are approved for this purpose.

Chlorine has been widely used as a disinfectant since the early 1900s. Chloramine and chlorine dioxide are two similar alternatives to chlorine.

Keep in mind that all chemical disinfectants cause DBPs. Utilities must balance the need to protect the public from water-borne illnesses while keeping DBPs at safe concentrations. Efforts began in the late 1970s to manage potential health risks associated with DBPs without compromising disinfection.

Utilities can control certain factors that influence the production of DBPs such as the amount of disinfectant used and the amount of organic material or minerals present during disinfection. Other factors such as temperature, pH and reaction time also affect DBP production.

Under the Safe Drinking Water Act Amendments of 1996, the USEPA created the Disinfection Byproducts Rule Stage 1 and 2 . This rule regulates acceptable levels of the DBPs mentioned below.

  • Trihalomethanes (THM) are a group of compounds that form when chlorine and chloramine react with organic matter, such as decaying plant material, present in source water. Surface waters, like lakes and rivers, may be especially high in organic matter because of plants and animals living in or near the water. The EPA regulates THMs at a maximum annual average of 80 parts per billion.
  • Haloacetic acids (HAA5) are a group of five chemicals formed during disinfection with chlorine and chloramine. The EPA regulates HAA5 at a maximum annual average of 60 parts per billion.
  • Bromate forms when ozone used for disinfection reacts with bromide naturally occurring in source waters. The EPA regulates bromate at a maximum annual average of 10 parts per billion.
  • Chlorite is a potential by-product of chlorine dioxide disinfection. The EPA regulates chlorite at one part per million.

NOTE: One part per billion is the equivalent of half a teaspoon of water in an Olympic-sized swimming pool. One part per million is the equivalent of one drop of water in 16 gallons.

For more information about the level of DBPs in your water, see your local utility’s annual Consumer Confidence Report. If you have concerns about a particular DBP, contact your local utility. Furthermore, some DBPs can be reduced through the use of home filtration devices.

If you are selecting a home treatment device for any purpose, it’s good practice to select a device that has been independently certified to address the issue of concern. NSF International, the Water Quality Association, Underwriters Laboratories and CSA International all certify home treatment products for removal of contaminants and to address taste and odor problems.