That's my next venture, although I've got some conflicting info on the legalities in my area. I figure when I get closer to being able to set it up, I'll get a little more serious about the legal research.
A couple of summers ago, the drought was so bad that our rain barrels were dry by the end of May, and didn't get full again till fall. We hauled water for the fruit/nut trees and perennials, but let the garden burn up.
We are on a well, so we do conserve water as much as possible. Don't want to run it dry.