The break happened around 3:30 a.m. on Van Ness Avenue at Broadway. Crews rushed to reopen one of the city's major thorough fares for Monday morning's commute.
The break sent water gushing down Van Ness and service was cut off to three apartment complexes for several hours while other customers experienced low water pressure.
"We can't determine the cause of the failure other than these are really old pipes the pipes in this road are probably 100-years-old, and just like someone's body they break down over time," San Francisco Public Utilities Commission spokesperson Christina Kerby said.
All but one northbound lane of Van Ness Avenue between Vallejo Street and Pacific Avenue was closed until the street was repaved. The intersection was completely reopened at about 8:00 a.m. on Monday.