The rupture of the 18-inch cast iron pipe occurred between 5 p.m. and 6 p.m. Friday, leaving the island without water service until 7 a.m. this morning, according to SFPUC spokeswoman Alison Kastama.
Although there is no evidence of water contamination, repairs and testing will be ongoing until Monday with a boil water notice in place, Kastama said.
Those who do not purify tap water before drinking risk a stomach or intestinal illness from possibly contaminated water, according to Kastama.
Water is available in residences for non-potable use -- such as toilet flushing, showers, and clothes washing -- but to drink water residents must boil or pick up water from two water trucks available on the island until the boil notice is lifted Monday.
Residents can bring clean water containers that can hold as much as 5-gallons of water to 12th Street and Avenue D, as well as at Gateview Avenue and Mason Court, Kastama said.
Kastama said the rupture appears to be the result of an aging pipe that is likely an original pipe part of the infrastructure built in the 1930s when the U.S. Navy inhabited the island.
The main that broke is the single water source for the island, she said.
Yerba Buena Island was not affected by the main break. Tap water on that island is safe to drink.
More information about the Treasure Island water emergency may be found at http://sfwater.org/index.aspx?page587.