I had three thoughts about this proposed transformation. It looks like there is willingness, and it is a pretty simple closed system. The author clearly spent a lot of time thinking about it.
- Hold some teaching sessions before the changeover. Hold at least three meetings, issue paper shares and let people game out a few water years. This is a big change, so people should get a chance to try it out and practice.
- Given that the internal rate of return from holding a water rate averaged well over 15% a year (pg 7), why give out grants for system transformation (recommendation, top of page 27)? Those should be loans, not grants.
- What are the metrics for success? How do we know if we have won? Self-assessed community happiness before and after this switch? Community satisfaction with water rights system? If the springs start flowing again? If the groundwater basin comes into sustainability without people shooting each other? Total acres farmed? Level of farm debt? Biodiversity index? You know, my mother is a statistician and my father is a scientist. Either of them would disown me for doing an experiment without explicitly stating what I am testing up front. How can we assess whether “the market” worked if we aren’t told up front what exactly it is trying to achieve. Before doing this, be very clear about what will be better in Diamond Valley when the system is up and running. (If I lived in Diamond Valley, I’d want to be happier after the switch than before.) Running this experiment and fishing around for improved metrics afterwards is scientific fishing, nearly as shameful as data mining. You would no longer be welcome at my parents’ table if you were guilty of scientific fishing.
On the public record 
I understood success for Diamond Valley to be avoiding the state taking a permanent interest in managing the water by bringing total use within sustainable yield. Young says that requires a 50% reduction in current use, which seems like a large number. Low flow toilets probably won’t be much help. Instead, it looks like share allocations are proposed to decrease gradually over a period of years which would let users gradually find equilibrium.
I think you’re right, that low flow toilets won’t do the job. It is an ag area, where nearly all of the water goes to irrigation. From the description, there are some potential gains for improved irrigation management (from 4af/a to 2.5af/a), but it looks to me like land will come out of production to end the overdraft.
The conversion and running of the market is itself a substantial state intervention, but it might feel different than a zoning decision or adjudication or water rights curtailment.