The San Francisco Public Utilities Commission received a report of the break at 5:30 a.m., said Catania Galvan, a spokeswoman with the agency. The break occurred in a 12-inch transmission line located at the intersection of 22nd Street and Potrero Avenue and did not impact local customers, she said. The agency is in the process of replacing the entire aging water main along Potrero as part of its water system improvement program, she said.