LOS ANGELES (CBSLA.com) — A report on what it would cost to earthquake-proof L.A.’s water supply is causing an aftershock through City Hall.

The Department of Water and Power’s findings show the cost could run as high as $15 billion.

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But Mayor Garcetti’s office denies it has any intention of asking DWP ratepayers, the citizens of L.A., to hand over that kind of money.

When the area is hit by a long-overdue massive earthquake, also dubbed the “Big One,” the Northridge Hospital Medical Center is one of the few places in the city where the water may still be flowing.

In January, the DWP spent $10 million replacing two miles of the facility’s old underground water piping with earthquake-proof pipes.

It was one of five pilot projects in L.A. and hailed by Garcetti as the first step in a much bigger job of outfitting the city with pipes that could stand up to the “Big One.”

But to complete the job citywide would involve installing 7,000 miles of water pipes, which would ring in at an estimated $12 to $15 billion, according to a DWP report released in the fall.

U.S. Geological Survey spokesperson Lucy Jones, who acts as the mayor’s science advisory, says a large earthquake could leave residents for at least

“How long would you be willing to stay if you couldn’t take a shower for a month?” Jones said.

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But taxpayer and DWP watchdog Jack Humphreville says he doesn’t think DWP customers will cover that astronomical price tag.

“Well, $15 billion is essentially twice the amount of the assets the Department of Water and Power has in its water system right now,” said Humphreville, who serves as a member on the Greater Wilshire Neighborhood Council. “So, to answer the question, I don’t think it’s going to fly. I think you’d have an absolute riot if you’re going to triple rates like they did in San Francisco. The [San Fernando] Valley would explode, just explode.”

In San Francisco, water rates reportedly tripled after the city embarked on a project to earthquake-proof its water system at a cost of about a third of the L.A. estimate.

Garcetti’s office and DWP insist they’re not asking for $15 billion and not launching a citywide earthquake-proofing campaign any time soon.

Instead, officials say pipes already scheduled to be replaced will be switched with earthquake-proof pipes gradually over the next three decades.

“The estimate includes double counted costs and was very preliminary. A build-out with earthquake pipes would span many decades as well with any costs also spread out over decades,” DWP Communications Director Joseph Ramillo told CBS2/KCAL9’s Dave Bryan.

The DWP says some of the funding may come from state bonds. Humphreville says that’s unlikely.

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In the meantime, the DWP says they’re focusing smaller pilot projects, such as the one at Northridge Hospital.