SUNOL -- Should calamity strike, the hundreds of thousands of people who depend on the Sunol Valley Water Treatment Plant not only will have water to drink, they'll have it for up to two months, after recently completed upgrades to the East Bay facility.

While hopes are that the plant, part of the San Francisco Public Utilities Commission's Hetch Hetchy Regional Water System, would rarely be asked to carry such a heavy load, preparing it for a worst-case scenario in earthquake country was the project's main purpose, officials said.

"Should Hetch Hetchy water supplies become unavailable for any reason, this plant now enables us to supply the minimum demand of water to our customers, especially those in the East Bay and South Bay," said Betsy Lauppe Rhodes, a SFPUC spokeswoman. "Without the upgrades to this plant, that reliability would not be there."

Utility and regional officials now aim to celebrate the $140 million project with a private ceremony and plaque unveiling Friday morning.

The plant was constructed in 1966, on 3.2 acres in Sunol Valley, east of Interstate 680. The facility's footprint now is 9 acres and it treats water used by hundreds of thousands of customers in Alameda and Santa Clara counties, Rhodes said.

Construction on its upgrades started there in 2010, and finished a month ago, while the final touches -- such as basic equipment testing -- continued throughout the past few weeks, Rhodes said.

The plant can now provide 160 million gallons of water per day for up to two months in case of emergency. Previously, that level of service would run out after only a matter of days.

The plant now includes equipment that has either been retrofitted or built from scratch to increase its efficiency in treating the water before distributing it to customers, officials said.

"We've increased the filtration's system capacity, which is now 16 gallons per minute," said Ravi Krishnaiah, senior project manager for SFPUC. "That's a 20 percent increase."

Krishnaiah, has been working on the plant upgrade since 2005, when it was just in the conceptual stages. "It's been gratifying to see something built from day one," he said. "It takes a whole team."

The facility's new features include a reservoir that can hold 17.5 million gallons of treated water, and a 3.5 million gallon tank, in which chlorine is injected in water during the treatment process.

The upgrade is one of SFPUC's 82 infrastructure improvement projects, in which $4.6 billion is being spent to repair, replace and seismically upgrade the water system's aging pipelines, reservoirs and dams.

The Hetch Hetchy Regional Water System serves 2.6 million customers in Alameda, Santa Clara, San Mateo and San Francisco counties. The system's pipelines is about 167 miles long, stretching from the Hetch Hetchy Reservoir in Yosemite National Park to the Bay Area.

Harlan Kelly, SFPUC's general manager, said the price tag of the series of improvement projects is worth it. "There would be $8 billion in impacts if we're without water for just 30 days," he said. "We've been successfully implementing these projects. Now we can deliver water in a lot of complex and dire situations and, to me, that's all very good."

Contact Chris De Benedetti at 510-353-7011. Follow him at Twitter.com/cdebenedetti.