With final upgrade, S.F. water system ready for the Big One

San Francisco residents shouldn't go thirsty when the next big earthquake hits.

That's because the Public Utilities Commission just finished $445 million worth of improvements to make the city's water system more seismically safe. A retrofit of Sutro Reservoir, the last of 35 projects in San Francisco, was finished this month.

The upgrades are among the 83 projects that have been completed or are under way in seven Bay Area counties as part of the $4.8 billion upgrading of the Hetch Hetchy water system's aging infrastructure. What's called the Water System Improvement Program is one of the largest water infrastructure programs in the nation.

The improvements are intended to prevent pipelines from snapping and reservoirs from cracking when the ground starts rumbling.

"We all know it's not a matter of if another big earthquake occurs, but when," Daniel Wade, director of the project, said. "We looked at the vulnerabilities of the system and realized we needed to ensure we could continue to deliver water to 2.6 million people during a seismic event. It was a race against time to get these projects implemented."

The Water System Improvement Program was funded by a bond measure approved by San Francisco voters in November 2002, but the first project didn't break ground for two years. Construction started at Summit Reservoir atop Twin Peaks in San Francisco in 2004, marking the start of more than 10 years of construction.

Since 2002, rates have tripled for both retail customers in San Francisco and wholesale customers that serve Alameda, San Mateo and Santa Clara counties.

"San Francisco is in a much better place now," Wade said. "We’re safer today than we were yesterday. This is the largest and most important project that the Public Utilities Commission has ever done."

Larger regional projects, like the Calaveras Dam replacement in the East Bay, will take three additional years or more to finish.

The Hetch Hetchy water system, which stretches 167 miles from Yosemite to the Bay Area, crosses three major earthquake faults — the San Andreas, Calaveras and Hayward — and a number of smaller ones. It feeds into 1,200 miles of water pipes in San Francisco, many of which are more than 100 years old.

The project is strengthening those pipes with new ball-and-slip-joint Japanese technology, which allows them to be jostled more than 6 feet or to compress without snapping. They’re the largest joints ever manufactured.

"There are two ways to design something to withstand an earthquake: You can make it extremely strong or extremely flexible," said David Briggs, local and regional water system manager for the PUC. "The magic in our new design is not the pipe but the joints. They allow a lot of give in lots of directions, so if the ground shakes, the pipes will not break apart."

The PUC learned this lesson the hard way during the 1989 Loma Prieta earthquake. Six blocks of the distribution system had to be valved off in its aftermath, Briggs said.

"That earthquake spawned a lot of change," said PUC General Manager Harlan Kelly, who oversaw the development of the program. "But we continue to learn from the past. People still remember how our city was destroyed by lack of water in the early 1900s. I think a lot of people were very concerned that our system wasn't ready should the next big one hit. It is now."

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Just because this project is wrapping up doesn't mean the work is over. The PUC will continue to replace old pumps and pipes to ensure they are able to deliver water within 24 hours.

"We’ve done a lot, but there are still areas that are old," Kelly said. "It's a never-ending task. We have been very successful, and I’m pleased with how everything turned out. I think we’ll all sleep easier at night knowing the city's water system is ready."

Lizzie Johnson is a San Francisco Chronicle staff writer. E-mail: [email protected] Twitter: @lizziejohnsonnn