The 1967 8-inch pipe burst shortly before 2 a.m. near North Tampa Avenue and Topham Street, causing a massive geyser to shoot up into the sky and flood the area.
LADWP crews said the incident would take several hours to repair.
About 20 customers were affected by the rupture, LADWP officials said.
Tampa Avenue from Topham to Oxnard streets was expected to be closed on the southbound side for several hours.