The water rights laws cannot be underestimated. This is mostly the result of the 1983 case National Audubon Society v. Superior Court [1]. Based around the public trust doctrine this case originally was about LA draining water from feeder streams to Mono Lake. The real effect has been many counties using this ruling as basis for restricting landowners from selling water from their properties outside the county. Hence farmers either let it go to no use or on lower value crops.

As for the rainwater issue, well they engineered themselves into that but that cistern idea was great.

[1] https://en.wikipedia.org/wiki/National_Audubon_Society_v._Su...