I've been reading about water in the American Southwest, mainly LA and Colorado River.
It's probably good to remember "Chinatown" was a movie NOT a documentary, so forget the film and it's characters.
LA receives about 40 % of it's water from the Colo and the reservoir above Parker Dam.
The Imperial Valley agriculture farms utilize about 50 % + of their water needs.
There are well over 1,000 + dams and a separate 1,000 + reservoirs in Callie alone.
The Commissioners of the Electric & Water boards are generally politicians, since the Chairman's yearly salary is $ 750,000 a year ! That tells you all you need to know !
They are operating power plants for electricity built 100 years ago !
To the best of my research they lose 100's of millions of gallons daily into the Pacific. I am unsure if this is treated water or not. For example, Manhattan loses 100-300,000,000 millions of untreated "water" into the Hudson River as their waste treatment plants are over loaded beyond capacity, if it rains.
I was unable to find any large scale desalination water plants working or planned in LA.