Penguinsix on youtube (lives in DC, and takes footage of monuments and goings on there) mentioned that the DC authorities flushh hydrants etc after winter every year,and that they were reminding the residents of that and the water would taste a bit more of chlorine while they were doing this.

I believe the high tide was also on the books, as 6ft above normal.

The tunnels could be being flushed, under cover of the normal pipe maintenance, to keep the bad guys in place, stop them leaving ahead of the door to door..

Link to his most recent video
.https://youtu.be/-PHUnLM0fiM