In very rough numbers, here's what CA has for water supplies, which factors into what might happen in a reworking of the Compact:
About 42 maf (+/-) of developed water delivery systems, and the major pieces are these:
- LA Aqueduct: 0.4 maf to Los Angeles from Owens Valley
which has changed quite a bit by now since Mono Lake and Owens Lake both take chunks out of that for rebuilding the water level (which is not going well at Mono Lake) or dust control at Owens Lake (which isn't a lake any longer). i know that right now the Mono Lake part of the portion of the water they are trying to export each year is subject to how low Mono Lake gets and right now it is only a few feet above the complete cut off level where LA won't be able to take any water until the level comes up again. this past season being extremely dry and hot will make this decision happen even faster if we get a repeat of low rain and snow this next water year.
of course i'm hoping for a much better coming year.
- Plus there is massive groundwater use, leading to serious overdraft in places, notably the southern San Joaquin Valley. In all the central valley has groundwater storage capacity of nearly 700 maf, but it's been used hard over the decades and going down fast. Many other smaller basins exist around the state.
ground water recharge is a major topic right now because if you get a good water year and have the infrastructure for it you can capture and spread water out to soak in. if you include that with recycling projects which also reinject water from recycled waste water then you've got a chance of at least stopping declines, but somehow you have to get the people who are pulling too much water from the ground via wells to get their use in balance with the actual recharge rate. this is all a work in progress in CA and there's many years yet of wrangling and working on this to get it all back into some semblence of balance.
having seen what can be done in very arid climates with recycled water and being careful i think CA has a long ways to go and a lot more room yet to get there.