Those mysterious brick circles you see on streets? They are cisterns — a form of ancient technology adopted after the 1906 earthquake to aid firefighting.
We all know about the fires that ravaged the city after the 1906 earthquake, made worse due to the rupture of water and sewage lines. Firefighters — then on horse and carriage — were hindered by the massive amounts of rubble and were unable to navigate the city efficiently to bring water to the sites.
The solution to this issue was called the Auxiliary Water Supply System; a plan that included fireboats, seawater pumping stations, and a system of long-term storage cisterns, allowing the city to have easy access to a network of water sources.
Here’s what they look like underground — pretty cool!
SF Water Power Sewer also tweeted this:
When u see bricks laid in a circular pattern in the middle of the intersection, THIS is what ur standing on top of. pic.twitter.com/Dzf1dyuoVg
— SF Water Power Sewer (@SFWater) May 2, 2015
However, it’s been pointed out that this isn’t one of the underground water cisterns, but rather an above-ground tank on Jones Street.
You can easily spot them throughout the city based on the red brick circles, as well as the manholes labeled CISTERN S.F.F.D.
But, for reasons unbeknownst to me, the Outer Richmond and Outer Sunset have brick squares instead of circles over the cisterns. San Francisco loves to keep things weird, I guess.
Currently there are over 170 independent underground water cisterns, varying in size from 75,000 gallons to over 200,000 gallons. Total storage capacity? Over 11 million gallons.
Click through the map below to find all the locations of cisterns in San Francisco:
Want to learn more about the cisterns? Check out this video below from the Exploratorium.
Featured Image: Ron’s Log