Of course, it's also probably a bad idea to plant water-thirsty stuff in a desert too. You plant what the climate and area supports.
Agriculture needs big reform here. Either cut it out, or make them pay their big share of water. But I guess nobody wants to buy a 50 dollar bag of almonds or pecans.
Personally, I might miss pecan pie once a year, but otherwise wouldn't even notice if both products ceased to exist.
I also saw that drewnick also posted that San Diego has a desal plant. That one sounds small - but I could see that scaled up x10, and then drop 20 of them along the coastlines.
Reclamation should also be definitely part of the overall plan too. But if the water input is gown that far down, no amount of reclamation will fix low source.
The salt has to go somewhere, and brine (concentrated salt water) is harmful to the environment and wild-life. I imagine the only effective way to handle it is to designate a deep water area that is politically acceptable to 'sacrifice' and pump the output entirely to that site. This is of course going to be extremely energy intensive and also will probably leak frequently as earthquakes and ship anchorage destroy the pipe.
Any form of thermal based power generation is going to have similar issues with it's cooling water (which is required in the heat differential that produces useful energy). Cars have radiator fans and waste heat from the engine for this exact reason.
Radical changes to reduce the quantity of water lost to current uses are probably required. I suspect one of them might be to boil the hell out of some of the waste treatment water that's clearer, or even as a distillation method, and send it off for use in recreation field watering and some farming where that makes sense. Lawns as a decorative feature or social status symbol should be banned. Greenhouses and Solar Updraft Tower hybrids ( https://en.wikipedia.org/wiki/Solar_updraft_tower ) might be a required conversion for farming regions.
So three of these plants would be approximately 1% of the water allocated in the original Colorado River compact.
California exports hay (grown on Coloradio River compact water) to other countries, including China and the Middle East. [0]
[0] https://www.desertsun.com/story/news/environment/2017/09/28/...
"The company announced in January 2016 that it paid $31.8 million for 1,790 acres. Some of its fields run alongside the Colorado River.
The company grows hay for cows in its dairy in Saudi Arabia, where the monarchy has set a policy of growing less alfalfa, wheat and corn to reduce pumping of groundwater from the depleted aquifers of the Arabian Peninsula."
While I agree the pitfalls of unchecked Capitalism are rather dire, you have to realize this business model is only possible because of USDA subsidies; under no other circumstances could this be a profitable endeavor if ti were left to Market forces alone, were it not for the State offsetting the obscene expenses it simply wouldn't be possible.
Furthermore, insuring these crops should be a matter for those respective nations and a premium should be placed on them as that is their final destination--especially since the House of Saud refuses to use it's own water but expects CA to use it's fertile soil and limited water supply to feed its dairy cattle.
When I worked in Carlsbad driving in from Southern OC, I remember seeing the construction for Poseidon, it was in the midst of the financial crisis but Carlsbad is an affluent city with mainly older residents and I recall thinking to myself: these guys know how to spend their money right.
If I recall correctly Poseidon supplies not just all of Carlsbad but also to the greater San Diego area and parts of Riverside and OC and is on track to recover it's costs ahead of schedule, right?