Washington Aqueduct begins annual chlorination period to facilitate water system disinfection, improve water quality

U.S. Army Corps of Engineers
Published March 25, 2024

From March 25 to May 6, 2024, Washington Aqueduct will temporarily switch disinfectant in drinking water from chloramine to chlorine to aid in cleaning water distribution systems and improve water quality. Water will remain safe to drink and use throughout this purification process, although the public may notice a slight change in taste and smell.  

This process, which is used by water utilities nationwide, allows local water authorities to clean pipes, or “flush the system,” from biofilms, the predominant mode of microbial growth found in drinking water distribution systems that can lead to water quality problems and pipe corrosion if not controlled. Biofilm can become accustomed to the usual chloramine disinfectant. By using free chlorine as a preventative maintenance measure temporarily, Aqueduct staff reduces the occurrence of biofilm as well as nitrification.  

Chlorine is a stronger disinfectant than chloramine and as a result, some water users may experience a slight change in taste or odor of their water during this period, including a noticeable “chlorine odor” and slight discoloration. This taste and odor do not pose a health risk and should lessen after a couple of weeks. Chlorine levels will continue to meet or exceed all EPA safety standards and requirements throughout the purification process.

The Washington Aqueduct collects, purifies, and pumps an average of 150 million gallons of water per day at two treatment plants in the District of Columbia for its three wholesale customers - DC Water, Arlington County, and Fairfax Water. We encourage water users to visit their respective water provider’s website for additional information, including recommendations on how they can reduce the taste and smell of chlorine during this period.

For more information on the Washington Aqueduct, go to http://www.nab.usace.army.mil/Missions/Washington-Aqueduct/

Dalecarlia Water Treatment Plant, Washington Aqueduct 


Additional Information

Baltimore District delivers vital engineering solutions in collaboration with its partners to serve and strengthen the Nation, energize the economy, and reduce disaster risks. Headquartered near Baltimore’s Inner Harbor, Baltimore District provides design, engineering, construction, environmental, and real estate expertise to various important projects and customers. This support spans five states, the District of Columbia, overseas, and the Susquehanna, Potomac, and Chesapeake Bay watersheds. These civil and military missions and diverse engineering services support communities and warfighters while addressing the ever-growing list of emerging national security requirements and ultimately protecting the Nation.


Cynthia Mitchell
443-240-5019 (cell)

Release no. 24-005