EBMUD workers were already in the area conducting routine maintenance shortly after 8 a.m. Tuesday when the pipe broke near the corner of South Main Street and Olympic Boulevard, district spokeswoman Andrea Pook said.
Pook said the valve break was not caused by the maintenance work.
A handful of businesses in the area were without water Tuesday afternoon because of the pipe break, and a few nearby stores sustained some water damage, Pook said.
EBMUD risk management teams were responding to those businesses to minimize the damage, she said.
Pook said that crews expect to have the pipe repaired by this evening, but that until that time, drivers in the area should expect some delays.
Walnut Creek police have announced road closures on Main Street between Mount Diablo Boulevard and Botelho Drive and on Olympic Boulevard between Locust and Main streets.