Liberty Reservoir is located on the North Branch of the Patapsco River on the boundary between Baltimore and Carroll Counties. It collects water from a 163.4 square mile drainage area that includes eastern Carroll County and southwestern Baltimore County.

Loch Raven Reservoir is north of Baltimore City and its watershed occupies Northern Baltimore County and small parts of Western Harford County and Southern York County, Pennsylvania. The source of reservoir water is Gunpowder Falls.

Loch Raven Dam was initially constructed in 1915 with a spillway elevation of 192 feet above MSL and raised to its current spillway crest elevation of 240 feet above MSL in 1923.

The reservoir capacity is approximately 23 billion gallons and the impounded area is roughly 2,400 acres. The Loch Raven Reservoir watershed is divided into eight subwatersheds: Beaver Dam Run (20.73 sq. mi.), Dulaney Valley Branch (3.24 sq. mi.), Gunpowder Falls I (24.56 sq. mi.), Gunpowder Falls II (1.77 sq. mi.), Little Falls (53.63 sq. mi.), Loch Raven Reservoir (59.31 sq. mi.), Piney Run (12.39 sq. mi.), and Western Run (47.67 sq. mi.).

Raw water from Loch Raven Reservoir travels through a 7.3-mile long, 12-foot diameter tunnel for treatment at the Montebello Filtration Plants in Baltimore.

Prettyboy Reservoir is in the northwest corner of Baltimore County and its 80 square mile watershed lies in northern Baltimore County and small portions of northeastern Carroll County and southern York County, Pennsylvania. Prettyboy Dam was completed in 1932, has a spillway crest elevation of 520 feet of MSL, impounds about 19 billion gallons of water, and covers about 1,500 acres.

The Prettyboy Watershed has been divided into four subwatersheds: Georges Run (15.85 sq. mi.), Graves Run (7.66 sq. mi.), Gunpowder Falls III (27.27 sq. mi.), and Prettyboy Reservoir (28.97 sq. mi.). Prettyboy Reservoir water is transferred to Loch Raven Reservoir via Gunpowder Falls rather than directly to Baltimore. The dam releases water as needed into the river channel, which flows into Loch Raven Reservoir.

Water from the Susquehanna River, approximately 11 miles north of Aberdeen near the Pennsylvania State line, is pumped via the Dear Creek Pumping Station to the Montebello Filtration Plants through the 38-mile long Susquehanna Conduit. This source is normally used during times of extreme drought when storage becomes depleted in the reservoirs. Earlier this year (2002) the persisting rainfall deficit gave sufficient cause to tap this water source. At this time, the City anticipates that with the exception of the first year of operation in 1966, this will be the most extensive use of the Suszuehanna supply experienced with in excess of 15 billion gallons expected to be withdrawn.

The Susquehanna Supply has a present capacity of about 150 million gallons per day with a planned future capacity of 200 million gallons per day.