California already has a massive system of rain water capture and extra-large cisterns we call reservoirs. The smaller the cistern the more expensive per gallon it is.
To me, you're rather out of touch. California depends upon the snowpack for a significant amount of its water supply -- and it ain't looking too good: http://cdec.water.ca.gov/cdecapp/snowapp/sweq.action
Perhaps these pieces of wisdom could offer some guide:
"When it rains it pours"
"Get it while the gettin' is good."
"Waste not, want not."
To me, rainwater capture can apply anywhere with a roof, a sky, and a mind to build cisterns.