Where does the water go?

An awful lot of stormwater just fell on the Washington area. DC Water shared this 2011 video about what happens to a raindrop after it falls in a storm until it gets to a river.

Stormwater has to pass through the Combined Sewer Overflow system, which mixes water and sewage. That is, unless and until DC Water digs new tunnels for stormwater (and, unfortunately, has to spend a very large amount of money to do it).