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Disinfection Byproducts in Drinking Water FAQ

Click on a topic below to view the answers.

What are disinfection byproducts?

When disinfectants like free chlorine and chloramines react over time with organic matter, such as decaying plant material in water, disinfection byproducts (DBPs) form. The Environmental Protection Agency (EPA) and the Virginia Department of Health (VDH) regulate the DBPs Total Trihalomethanes (TTHM) and Haloacetic Acids (HAA5).

The EPA has set a limit on TTHM at .080 mg/L and HAA5 at .060 mg/L as a locational running annual average. The Service Authority is required to take samples every three months from its chlorinated distribution systems. The sample results for TTHM and HAA5 in the Service Authority’s distribution system are consistently below the EPA limit, which VDH enforces.

Continuous exposure to high levels of DBPs have been linked to certain types of cancer. However, the World Health Organization has stated that the risk of illness from waterborne pathogens is at least 10,000 to 1 million times greater than the risk of cancer from DBPs. In addition, due to its chemical makeup, chloramines are less reactive to organic matter than free chlorine and thus produce less DBPs than free chlorine.

How is the Service Authority’s drinking water disinfected before it reaches customers?

Fairfax Water, which provides Service Authority customers the majority of their drinking water, uses both ozonation and chloramines in its disinfection process. Ozone is a gas produced when subjecting oxygen molecules to high electrical voltages. This process destroys bacteria and other microorganisms. Just before the water leaves the treatment plant, Fairfax Water adds chloramines. Chloramines, which are the combination of ammonia and chlorine, form a stable bond that keeps the disinfectant more stable throughout the entire water distribution system. The City of Manassas, which provides drinking water for some of our western Prince William customers, also adds chloramines for disinfection. During the spring months each year, the Service Authority’s water providers disinfect drinking water with free chlorine, which is a stronger disinfectant, in order to deny bacteria the ability to form resistances to the usual disinfection treatment process.

Who establishes the quality standards for public water systems?

The EPA sets national regulatory standards to protect the public health. VDH enforces these standards for drinking water systems in Virginia. On both a monthly and annual basis, the Service Authority submits its water quality test results to VDH to ensure that the utility is providing water that meets all federal and state drinking water regulations. The Service Authority must notify VDH and its customers immediately if a water quality violation were to occur, and then coordinate with VDH to take timely corrective action.