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FAQ - September 10 Flooding FAQs

During very heavy rainfalls, the stormwater system can become overwhelmed by a very heavy volume of water. When that happens, some stormwater and sewage in a combined sewer system can be forced back up and into basements as the water overwhelms the sewer lines in the street. The system is impacted by the amount of impervious surface and the amount of rain that falls during a short time period. The rain volume on Thursday exceeded two inches and in some cases was falling at a rate equivalent to a 100 year storm. The DC Water system performed as designed but it cannot prevent all flooding.

In most cases, the DC Water sewage and stormwater system can handle the volume without flooding. Flooding will only occur when the volume exceeds the capacity of the sewer system. Construction of a series of deep underground tunnels known as the DC Water Clean Rivers Project is already vastly reducing the incidence of flooding and sewage overflows across the city. It’s also reducing pollution into the Anacostia River, which is where the excess sewage and stormwater flows during extremely heavy rains. More information about the tunnel system and how it is reducing flooding can be found by visiting

DC Water is conducting a review of this wet weather event to determine the causes of property and surface flooding in impacted areas of the District. Once that report is written, DC Water will share the results with all residents and with other District agencies and we will post it on our website.

DC Water is continuing to modernize and rehabilitate its sewer and pump station infrastructure every year. The city inherited a very old system from the federal government and we work every year to invest in reliability and other improvements. In addition, the Clean Rivers Project is steadily reducing flooding incidents and as additional tunnels come on line in 2023 and 2030 there should be even more reduction in overflows and flooding. The First Street Tunnel in Bloomingdale and the lower leg of the Anacostia Tunnel are both in operation and are functioning as overflow storage during heavy rains. For example, the Anacostia tunnel can hold more than 100 million gallons of sewage and stormwater and the First Street tunnel can hold 8 million gallons.

A virtual Town Hall to discuss the flooding with residents is tentatively scheduled for Wednesday, September 16. During that meeting, DC Water will review the flooding and discuss options for residents. More details will be shared once the meeting is scheduled.

DC Water General Manager David Gadis announced this weekend that DC Water will expand the backwater valve rebate program for residents in heavily flooded areas impacted by the Thursday storm.

More information about applying for the backwater valve program can be found on the DC Water’s website at Applications are typically resolved in about a week after consultation with engineers to determine if the valve will be of use to your property.

For questions related to the impact of this event, please reach out to Barbara Mitchell in DC Water’s Office of Government & Legal Affairs.  Ms. Mitchell can be reached at and 202-320-5299.

The District of Columbia Homeland Security and Emergency Management Agency and the Mayor's Office of Community Relations are canvassing impacted neighborhoods to gather information about the scope of resident damage. They encourage residents who have not yet completed a damage survey to complete it as soon as possible. You can find the link here:

We recommend you seek immediate relief from your homeowner’s insurance to assist with limiting further property damage.  Residents who wish to may file a claim for damages by visiting the DC Water website at or call 202-787-2050 for information regarding the claims process and what to expect.