Spring Flushing of the Water Mains

As part of the annual maintenance program on March 23th, 2020 Fairfax Water and the Washington Aqueduct, Loudoun Water and the City of Manassas switched from chloramine to chlorine to disinfect their water. During this time, Arlington Department of Environmental Services, DC Water, the Prince William Service Authority, Loudoun Water and Fairfax Water began flushing their water distribution systems. Each spring these water distribution companies flush their water mains by opening fire hydrants and allowing them to flow freely for a short period of time.

Fairfax Water will disinfect with chlorine from March 23th to June 17th and the water systems the flushing of the water mains in Fairfax and Prince William will occur during that time. Crews from the Service Authority and Fairfax Water will open hydrants throughout their service area in brief intervals in order to draw water more forcefully through the distribution system. This helps to dislodge sediment that may have collected in water mains over the past year. In DC, the flushing will occur from March 23 through May 4, 2019. DC Water purchases treated drinking water from the Washington Aqueduct. Loudoun Water announced they were starting their program on March 17th .During the temporary switch to chlorine, the Washington Aqueduct will continue to add a corrosion control inhibitor during this temporary switch to prevent lead release into the water system.

For most of the year, chloramines, also known as combined chlorine, is added to the water as the primary disinfectant. During the spring the water treatment plants for Fairfax Water, and the Washington Aqueduct switch back to chlorine in an uncombined state, commonly referred to as free chlorine. This free chlorine reacts with sediments suspended during flushing and kills bacteria that may be in the bio-film that forms on the pipe walls. Many water chemistry experts believe this short exposure to a different type of disinfectant maintains a low microbial growth in the bio-film and improves the quality and safety of the water.

This change in disinfection is an annual program to clean the water distribution pipes and maintain high water quality throughout the year. The U.S. Army Corps of Engineers Washington Aqueduct provides water to the District of Columbia, Arlington County, and other areas in Virginia. Fairfax Water provides water to Fairfax County and parts of both Loudoun and Prince William County. WSSC does not switch their disinfectant.

You may notice a slight chlorine taste and smell in your drinking water during this time, this is not harmful and the water remains safe to drink. Also this disinfection is unrelated to the coronavirus pandemic. You may want to use filtered water to drink or leave an open container of water in the refrigerator for a couple of hours to allow the smell to dissipate. Refrigerator filters remove chlorine so you do not have to worry about ice. Water customers who normally take special precautions to remove chloramine from tap water, such as dialysis centers, medical facilities and aquarium owners, should continue to take the same precautions during the temporary switch to chlorine. Most methods for removing chloramine from tap water are effective in removing chlorine. The annual chlorination is important step to remove residue from the water distribution system.

Flushing the water system entails sending a rapid flow of chlorinated water through the water mains. As part of the flushing program, fire hydrants are checked and operated in a coordinated pattern to help ensure their operation and adequate flushing of the system. The flushing removes sediments made up of minerals which have accumulated over time in the pipes as well as bacteria on the bio-film. An annual flushing program helps to keep fresh and clear water throughout the distribution system. Removing the residue ensures that when the water arrives in your home, it is the same high quality as when it left the water treatment plant.

The final steps in the water treatment process is the second disinfection. For most of the year Fairfax Water and the Washington Aqueduct use chloramine as the final disinfection step in water treatment. However, during the spring of every year they use chlorine to disinfect and flush the delivery network. Free chlorine is better suited to remove residue that may have collected in the pipes and a coordinated opening of fire hydrants serves to flush the system.