The distribution system (referred to as the Central System) delivers treated water to Baltimore area consumers throughout the metropolitan area. The Central System service area is approximately 560 square miles and provides potable water to about 1.8 million people.

The system distributes water through a network of water mains ranging in size from three inches to twelve feet in diameter. Most of these mains are constructed of cast iron, but some of the larger mains are steel or reinforced concrete. Currently, more than 4,500 miles of mains are in service in the distribution system. These mains connect a series of pumping stations, reservoirs, and elevated storage tanks, which supply water to Baltimore City and parts of Baltimore County, Howard, and Anne Arundel Counties. Within the network of mains, five major pressure zones are maintained to provide adequate water pressure and supply to the consumers.

Under the present operating system, the Montebello Filtration plants supply water to the First Zone by gravity, and the Second and Third Zones by pumping. The Ashburton Filtration Plant supplies water to the Second Zone by gravity, and to the Third, Fourth, and Fifth Zones by pumping.