Throughout San Francisco, 175 underground cisterns still exist as part of a dedicated fire emergency system developed in 1908. Most of them can be identified by a distinctive brick circle on the road.
Following the 1906 earthquake, the Auxiliary Water Supply System
(AWSS) - a separate and distinct water supply system for fire
protection use only - was built. The system includes dedicated reservoirs, pump stations, fireboats, cisterns and hydrants. The cisterns are disconnected from the network, with no pipes, in the event of major damage to the distribution system.