I just got thru with a 2 hour on site chat with a rain collection expert who's been installing systems all his life, even does 3rd world collection systems in S. America, Mexico, etc. Lot's ot trenching, plumbing, 1 HP Grundfos pump, guttering, switches, electricity utility work, 20,000 gal. tank....the works and a rough estimate is under $30K. Wife is about to have a fit considering we have a well that has a potential output of 150 gpm for only pennies cost per day for electricity to drive the 1 HP pump.. Kicker is that well water is hard enough to make concrete out of - 800 + PPM TDS, mostly bicarbs of Mg and Ca.
Hasn't rain water collection caught on yet in Cali?