Estimates are over 60 billion gallons of fresh water were used annually for enhanced oil recovery in Kern County in recent years. A new law this year may help confirm this number. The water use is associated with oil production of around 105 million barrels annually. The water was used mostly for water flooding, steam injection, and fracking.
A barrel of crude (42 gallons) can produce around 30 gallons of diesel and gasoline. This number is probably smaller for the heavier crudes found in Kern County which also require even greater amounts of steam.
If these figures are correct, a little math shows that for every gallon of diesel or gasoline, around 20 gallons of water was used in the production of the crude (at least for Kern County crude).
If the average consumption for pickups and cars is 20 miles per gallon, then the average driver is using about one gallon of fresh water for each mile driven. If you drive a Prius you are still using nearly half that much water per mile.
Saving water during this drought may mean driving less and therefore driving down the price of crude even lower. Less oil production in Kern County means more water saved.