The primary source of drinking water for the City of Manassas is Lake Manassas.  Construction of the dam which impounds Lake Manassas was completed in 1969, and the lake holds 5.1 billion gallons of water when full.  Water from Lake Manassas is treated at its water treatment plant (WTP), which can treat up to 14 million gallons per day.  Treatment is performed through settling of suspended solids, filtration, and disinfection.  After disinfection, water is pumped to the distribution system.

The City of Manassas Water Distribution system has approximately 10,650 customer connections, and consists of 155 miles of pipe, 1,443 fire hydrants, 3,758 valves, four water storage facilities, and one booster station.  This infrastructure is maintained through routine flushing, valve exercising, leak detection, pipe replacement, and repairs.