Disinfectant Byproducts

When chlorine is added to the water to kill bacteria and other microorganisms, the chlorine reacts with naturally-occurring materials found in drinking water sources, such as rivers and lakes. These reactions can produce disinfection byproducts, some of which may lead to increased health risks if long-term exposure occurs. The U.S. Environmental Protection Agency (EPA) sets enforceable limits for two categories of disinfection byproducts in drinking water: trihalomethanes and haloacetic acids. The limit for total trihalomethanes (TTHMs) is 80 parts per billion (ppb) and the limit for five haloacetic acids (HAA5) is 60 ppb.

In November 2000, DC Water began delivering water with chloramines, instead of chlorine, to reduce the amount of disinfection byproducts in the water. The treatment change caused a significant decrease in disinfection byproduct concentrations. To date, DC Water has not reported any disinfection byproduct violations.

Health risks from disinfection byproducts are associated with long-term exposure at high doses. Therefore, test results are averaged annually for each sampling location. EPA requires testing every three months at 12 different locations in the distribution system. The annual average is calculated by using the data from the most recent quarter and the three previous quarters. The graph below displays the annual averages reported to EPA for the last five monitoring periods. The highest annual average of the 12 sampling locations is shown in the graph.

Disinfection Byproduct Results
Disinfection Byproduct Results

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