The average precipitation in California is about 20 inches (per year, and the relevant year for precipitation recording is July 1- June 30) with a recorded maximum of 40 in 1982/3 and recorded minimum of about 10, which is when we speak of drought, as in 2013/2014 season
For the particular cities can differ a lot and for example, last year Los Angeles had 6 inches while San Francisco had 12 inches in the last rainfall year (until June 30, 2014)