Standing at the corner of Grant and Vallejo, take a look at the manhole cover in the middle of the intersection (which is shown above), which is marked "Cistern." One of many water storage tanks buried under San Francisco's streets, this on is part of the multi-pronged approach to fire prevention, implemented after the 1906 earthquake and fire, when pipes broke and the fire hydrants failed.
The other pictures in this group show some of the fire hydrants found around North Beach. The hydrant with a ball on top was made to give firemen a place to tie up their horses, a type that is fast disappearing. The green top on the small hydrant denotes that it's connected to the cistern. the hydrant with a large, blue bonnet is connected to a pair of reservoirs atop Twin Peaks.