This is part of one of the oldest aqueduct and water reservoir systems in the USA. It was designed in the 1830's and then improved in 1960's by Army Engineers. There is a "Low Aqueduct Reservoir" and a "High Reservoir". It was all gravity fed from various underground tunnels reaching to the Potomac River and Falls Creek "pond" which is up stream from the Potomac River. The pillar-like structures which are shown in the video are support columns and were originally poured in the 1930's by the WPA, then reinforced in the 1950's. The tube-like structures which have numbers painted on the entrances are "mixing chambers" and "Abatement Capture" which provide reduction of water sedimentation and turbulence. The tunnels --- actually underground aqueducts --- run for miles under the city and the main line runs down the center of what is now Reservoir Road, NW, with branches off to various pumping and holding stations. Towards the South there is another large collection point near Buzzards Point around 2d and F Streets, SE, with the pumping station located underground inside the grounds of Fort McNair. The tunnels which used to run criss-cross around the center of DC were either destroyed or moved when the DC Metro Subway System was constructed. The Childrens' Hospital has hundreds of thousands of square feet of underground space -- 4 sub-basements -- including an elaborate survival area first built during World War II. It has armored vault doors, concealed air intakes and exhausts and separate power generation. They most likely use the boron-fusion generators and destruction machines provided by the Large Greys.