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What's the Story With the Little Building on Jones Street?

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From the Curbed inbox:

On the 1200 block of Jones there's this little building that's attached to a water tower. It's perfect and very out of place. What's the story there?This little building tucked back from the street at 1239 Jones is known as the Jones Street Tank and is part of the city's larger Auxiliary Water Supply System. The whole thing goes back to the 1906 Earthquake and Fire, which prompted the city to get a system in place in case another disaster ever occurred.

Auxiliary Water Supply System map [Photo: SF Planning (pdf)]

After the 1906 fire destroyed huge swaths of San Francisco, voters passed a bond issue in 1909 that created the San Francisco Fire Department Auxiliary Water Supply System – a fire hydrant gravity flow system that supplements the main city water system in case an emergency requires the SFFD to fight multiple fires simultaneously or the main system is damaged. The system works by gravity, where water from a ten million gallon reservoir atop Twin Peaks flows through two tanks on Jones and Asbury streets, and then through a separate hydrant grid down to two pumping stations on 2nd Street and in Fort Mason.

Auxiliary Water Supply System diagram [Photo: SF Planning (pdf)]

The Jones Street Tank and associated gate valve house were constructed in 1912 between Clay and Sacramento streets. The 35' tall tank holds a staggering 750,000 gallons of water, making it the largest west of the Mississippi at the time of its construction. It was designed to be used to fight fires in the "lower zone" (everything below 150' elevation above sea level) through special blue-capped hydrants. A bunch of water lines run through the valve control house to link up with the city's water utility line. There are 20 gate valves that act as on-off switches to the tangled knot of pipes connecting the tank to the system.

Jones Street tank diagram [Photo: SF Planning (pdf)]

It looks pretty complicated now, but was even more advanced at the time of its construction. The system acted as a driving force in rebuilding the city, since it assured fire insurance companies that such a disaster couldn't happen again. Pretty impressive, considering the system is running pretty much the same as when it was constructed over 100 years ago. The city updated a bunch of stuff in 2009, like seismic retrofits and replacement of old pipes, but it's essentially the same system. In fact, the two pumping stations were used during the 1989 Loma Prieta earthquake to pump saltwater into the system, helping provide water to firefighting efforts in the Marina.

Garden opening in 2006 [Photo: Nob Hill Association]

Never one to miss an opportunity to make something nicer to look at, the Nob Hill Association helped the SFFD design and plant a new garden in front of the gate valve house in 2004.
· Jones Street Tank is Nearing Completion [Municipal Record via Google Books]
· State of Auxiliary High Pressure Water System [The Adjuster via Google Books]
· Vintage Firehouses - Pumping Station No. 2 [Guardians of the City]
· Preliminary Mitigated Negative Declaration - San Francisco Auxiliary Water Supply System Seismic Upgrade (pdf) [SF Planning]
· San Francisco Fire Department AWSS Review - 1989 earthquake [Virtual Museum of SF]