The original distribution system, built as part of the construction of the aqueduct itself, served only a relatively small area of the city, as compared to the extent of water service now. Shown as a dashed line on the map, the original water-supply mains prioritized government buildings, such as the Capitol and the White House, and areas of concentrated population, like Georgetown. To ensure adequate pressure throughout the system, and to get water to places that were at higher elevation than downtown, the engineers built a series of "high service" reservoirs in high points around the city. Most have been demolished in modernization efforts. A few fragments of trident-shaped fencing, however, remain in the special collections of the Georgetown Public Library, which was built on the site of one of these domed reservoirs.
The modern system of water mains extends out to the District's limits, serving all residential areas and generally following the route of major roadways. Modern high-service reservoirs, indicated by a circular icon in the map, were built to serve the areas of the District at higher elevations.