Southern Californians use about 350 gallons of water per day per household (of 3). That's about 110 gallons/capita/day (gcd).
People in San Francisco use about 63 gcd, and people in the Bay Area use about 97 gcd.
Now many people are saying that it will be impossible for Californians to cut back their consumption 20% in this year (short run) or 20% by 2020 (long run). (Farmers will be able to cut back, of course, but the cost of the cutback is disputed...)
I'd say that they are wrong, if we take the average consumption of 140 lcd (37 gcd) in Australia as an example of what can be done.
In fact, its wrong as far as this San Diego lady is concerned -- she uses about 49 gcd, which is FAR less than what her neighbors use.
The crazy thing is that she actually has a small grass lawn!
Bottom Line: We can easily achieve "adequate" demand responses, and the best way to do so is by raising prices by a LOT for excessive (>100 gcd) water use...
hattips to JM and DW