I do not know the details either, but the stories talk about personnel not relasing the water? Sounds like someone turned off the spigot. Of course, as others have noted, the entire ocean was right there too.
See link @ #14
San Francisco has a gravity fed emergency water system, with separate mains to feed separate hydrants along with massive cisterns under intersections to draft water from if needed.
In the event the gravity system fails, they have pumping stations to pump salt water as a second to last resort. If those fail, they can use fire boats to feed the system.
Of course it is not ideal to pump salt water thru fire pumps, but as a absolute last resort it can be done.