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Disinfection Byproducts (DBPs)

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.

Quick facts about DBPs

- Disinfectants are important for killing harmful bacteria, viruses, and other microorganisms in drinking water.

- Over 200 million Americans currently drink water that has been disinfected.

- However, disinfectants react with compounds naturally present in source water.

- When disinfectants react with these compounds, new compounds known as disinfection byproducts (DBPs) are created.

- North American drinking water has very low concentrations of DBPs.

- The USEPA has not been able to link the low concentrations of DBPs in drinking water to health risks such as cancer.

- Research on the relationship between DBPs and cancer and other health risks is ongoing.

- All chemical disinfectants produce DBPs.

- Five categories of DBPs are regulated by the EPA.

- Utilities are required to report the concentrations of these DBPs in their annual Consumer Confident Reports.

- Some home filtration devices can remove DBPs.

All commonly used chemical disinfectants form DBPs. The EPA regulates five kinds of DBPs at levels that current research considers safe.

Health concerns

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.

Why disinfect?

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 20th 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 U.S. 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.

Types of disinfection

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-term to offer protection as water travels through the distribution system and into consumer’s homes. Secondary treatment is designed to prevent organisms from regrowing as 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 1900’s.

Chloramine and chlorine dioxide are two similar alternatives to chlorine. 
Each of these chlorine-based disinfectants has its strong points and may be the best choice depending on many factors. However, there are certain DBPs associated with all three.

Regulated DBPs

Under the Safe Drinking Water Act Amendments of 1996, the EPA 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.

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.

What can I do?

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. NSF International is a good resource for further guidance. 

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