San Francisco has an underground emergency water supply: How reliable is it?

SAN FRANCISCO (KGO) -- The fires in Southern California have many wondering how prepared San Francisco is in the event of a major catastrophe.

Sure, San Francisco neighborhoods have plenty of fire hydrants, but as we learned in Southern California, hydrants can run dry.

It happened to us during the 1906 earthquake. It's been a constant reminder.

In the last several years, San Francisco has added underground cisterns for a citywide total of 222, many holding up to 75,000 gallons of water. The largest is located near city hall with a capacity of more than 240,000 gallons of water.

"You can easily find them. There's a round circle of bricks used in main intersections," said Tony Rivera, the former assistant deputy chief for the San Francisco Fire Department.

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A few years ago ABC7 News was invited to go underground to check out the construction of one of the new cisterns. At the time, the older ones were also repaired and reinforced.

The important thing to know here is that they are completely unconnected from the rest of the water system, meaning if the regular fire hydrants run dry, firefighters have another source.

Then Fire Chief Joanne Hayes-White talked about the significance of these cisterns.

"Some people say well, you don't really use it on a regular basis, but I tell you when the big one hits, these will be invaluable," Hayes-White said.

You know what else San Francisco has, three reservoirs that feed high-pressure emergency hydrants. These are not your regular hydrants. They are independent and gravity fed, an ideal system because of our hills.

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"They have more robust mains that are made of ductile iron and steel. They are not relying on another source of water. This is like a system designed specifically for firefighting and used by our firefighters. Our apparatus, we have special equipment on board to access the water. It's something you won't see in any other city," Rivera said.

Each reservoir covers several neighborhoods. For example, the Twin Peaks reservoir feeds all of those big high-pressure hydrants with a black top. The Ashbury tank feeds the ones with the red tops and the Jones Street tank delivers water to all of the blue-top hydrants.

However, the high-pressure system does not extend to some neighborhoods like the Bayview or to the Richmond and Sunset Districts.

In a Civil Grand Jury report, it was recommended that the city expand the supply with a target completion date of no later than 2034.

Still, it was in those neighborhoods where most of the cisterns were added.

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Because redundancy is our middle name, San Francisco can also rely on fireboats to pump seawater into the high-pressure network.

That's what was used in the Marina during the 1989 earthquake to stop the fires from spreading.

Rivera describes our water emergency system as unique.

"When I was in my position, I had firefighters come from all over the world to ask me, to look at it, go to our pumping stations. They've never seen anything like it," Rivera said.