One BIG solution for Californias water situation

I won't call it a drought, I will say too many people living in an area with historical water shortages.
But this solution will cost nobody any water and yet it will save 10's of millions of gallons of water every day, in California alone. I figure if implemented in the USA it would save over 5 billions gallons of fresh water everyday.
The solution: A holding tank for bath water. It is then used for flushing the toilet with.