Should the lower rainfall amounts continue through the summer, there could be problems of urban water supply in Washington, DC and its surroundings. Unlike most American cities of comparable size, Washington does not have large storage reservoirs to augment low flows during droughts, reservoirs filled in seasons and years of normal or above normal rainfall. Instead Washington depends on run of river flows on the Potomac River, its major water source. The Potomac and tributaries are the source for almost all of the water consumed in Washington, DC and its Virginia suburbs. Part of the demand in the Maryland suburban counties is met from the Patuxent, a river that flows parallel to the Potomac but enters the Chesapeake Bay directly.All of the streams are dependent on precipitation falling in the two adjacent watersheds, rain and snowfall in a roughly 40,000 square km area
[By the way, the water restrictions in suburban Maryland noted a few days ago have been lifted as the pipe has been repaired, but the Washington Suburban Sanitary Commission is aware that much of its infrastructure is old and potentially at risk for failure. Meanwhile the Montgomery county seat of Rockville, which has its own water system, had declared an emergency and called on residents to curtail water use. That emergency caused by a water main break was ended earlier today. ]
The Washington DC Metropolitan area falls at a boundary in the (arbitrary) division of the US into climate regions. The Drought Monitor at the end of June from the University of Nebraska, Lincoln suggests that the Virginia suburban are at the early stage of drought.