According to The Los Angeles Times:

A water main break in the 1200 block of North Formosa Avenue in West Hollywood early Sunday morning flooded an underground parking garage and left more than two dozen customers without service, according to Los Angeles Department of Water and Power officials.

The break in a 12-inch cast iron water main occurred just before 5 a.m. and damaged the street. DWP officials were not immediately sure what caused the rupture.

A Times analysis of city data last year showed there had been 5,200 leaks in L.A. DWP pipes since 2010, and that two-thirds of those leaking pipes were installed before 1950.