SoCal, Orange County in particular, has one of the deepest aquifers in the entire country.
The problem is we just haven’t been getting any rain to replenish it.
That, and the fact that massive immigration from the 3rd world has vastly increased the population that is using the water that we do have.
...... Aquifers are much different that "Cisterns." Aquifers rely pretty much on the amount of natural rain that seeps into the ground and replenishes the water table. Cisterns, on the other hand, are for the most part artificially created Underground storage areas which would be greatly suited for arid regions when rainwater is directed and channeled for collection in them.
.... In Los Angeles for instance, we have the so called L.A. River which directs the rainwater mostly out to sea instead of collecting that valuable resource for future use.