The break of the 8-inch main was first reported about 1:45 a.m. Wednesday on the sidewalk along the 7900 block of Forrest Avenue.
The break is being blamed for causing a sinkhole that damaged the front steps of a house.
Police and firefighters blocked off the street while water crews got to work.
The main was shut down completely to be repaired.
40 to 50 properties are without water. Officials say service should be restored by mid-afternoon.