One million residents of Washington D.C., Maryland and Virginia get their drinking water from the Dalecarlia Reservoir, a remarkable 150-year-old system that works entirely on gravity power. Overlooking the reservoir is a beautiful old tower, completed in 1927 as a major step forward for water quality in the district.

The chemical treatment tower at the Dalecarlia Reservoir (originally known as the Washington Aqueduct’s Receiving Reservoir) has an industrial vibe par excellence, and boasts awesome views of the aquatic infrastructure below to boot.

Water enters the reservoir through a nine-mile underground conduit located under the median of Macarthur Boulevard (originally named Conduit Road). The original design cleaned the “raw water” in huge pools where sediment was filtered out, also by gravity, and the resulting clear water was piped out into the city.

The tower and adjoining filter building represented an exciting water treatment innovation: chemical filtration. A Washington Post report from 1927 gleefully described the “Super-Purity” provided by the “immense” filtration facilities. The public was once free to wander around Dalecarlia Reservoir but that came to an end amidst concerns of sabotage during World War II. Today only people with official business may visit the premises.