The contractor was working on the city's Sunset District Sewer and Pavement Renovation Project when the 8-inch line ruptured at Noriega Street and 20th Avenue around 8:30 a.m., San Francisco Public Utilities Commission spokeswoman Alison Kastama said.
Water service has been disrupted at businesses and homes on Noriega Street between 19th and 21st avenues. Service is expected to be restored sometime between 12:30 p.m. and 2:30 p.m., Kastama said.
SFPUC crews are on site and have isolated the break, she said.
The city's claims department is also on hand for any nearby businesses affected by the water service disruption, Kastama said.