Have you ever noticed those brick circles at intersections in SF? They mark the perimeter of SF’s 180+ water cisterns, an emergency firefighting tool that dates back to the 1850s.
Beneath each brick circle rests a 75,000-200,000 gallon reservoir that supplies firefighters with a crucial emergency water supply. These reservoirs were first built in 1852 in response to a series of seven severe fires that ravaged the city between 1849 and 1851, at the height of the California Gold Rush.
Unfortunately, the network of cisterns fell into disuse and disrepair in favor of water mains and hydrants. The catastrophic 1906 earthquake damaged water mains and cut off water transmission to SF for over 62 hours.
SF firefighters had to rely on City reservoirs alone, which were quickly exhausted. Without an adequate water supply to battle the blaze, fires raged across SF destroying approximately 25,000 buildings on 490 city blocks.
To address this vulnerability, old cisterns were repaired, and many new ones were built across SF as part of SF’s Auxiliary Water Supply System (AWSS). The AWSS system utilizes cisterns, fire boats, pump stations, and strategically placed reservoirs around SF.
The first ones were built with bricks, underneath they’re solid brick, which is where you get the brick ring from,” Ken Lombardi, Assistant Deputy Chief of the SF Fire Dept. told the Exploratorium. “The cisterns now are made with concrete and steel rebar. If there was an earthquake they’d be one of the safest places to be, if they were empty, because it’s just a solid underground tank.
SF’s Exploratorium put together an exceptional program on the cisterns:
Collectively, this system of cisterns holds over 11 million gallons of water. This is supported by three massive reservoirs that are solely dedicated to firefighting:
- Twin Peaks Reservoir: 10.5-million-gallon capacity
- Ashbury Tank: 500,000-gallon capacity
- Jones Street Tank: 750,000-gallon capacity
These massive emergency reservoirs are completely separate from the 11 reservoirs that provide drinking water to SF residents.
If you’re curious about cisterns near you, SF Fire has a wonderful interactive map that you can use to explore this underground world.