The 12-inch water main broke at around 2:30 p.m. The rupture might have been caused by a contractor working in the area, San Francisco Public Utilities Commission spokesman Tyrone Jue said.
As of 4 p.m., utilities workers were reducing the flow of water, and Jue said residents in the area should expect to have low water pressure throughout the evening. Repairs are expected to be completed by 10 p.m.
Two or three homes may have been damaged by flooding, Jue said. Sandbags are being used to block water from further damaging homes and drain water into the sewer system.