This is not just the story of California, but the entire US southwest. Unlike back east, where water is subject to municipal authority and policy (thus allowing a town/city/county/state to decide what the best way to use the water is, especially in times of actual or imminent shortages), the western states ended up with this absurd "water rights" concept that prevents effective policy making.
Eh, back east water isn’t life and death - in the sense that for the vast majority of the east coast, everyone has plenty unless you’re a gigantic super metropolis.
In the west, water is scarce and the most limited resource in most areas - and literally life and death.
An old saw here is, ‘whiskey is for drinking, water is for fighting over’
You'd have said that in the UK and Western Europe if you're less than 100 years old ... until this summer. Sure, it may not literally be life or death the way it could be if you were lost on foot in the deserts of Nevada, but the prospect of running out of water for agriculture in certain parts of what has hitherto been a well-watered part of the world became quite tangible this summer.
The old dividing line for "agriculture without irrigation" was the 100th meridian. It has already moved at least two degrees east, and there are some forecasts that predict that climate change could move it as far as the 90th. So "the east" is a bit of a mutable concept at this time.
‘literally life and death’ is exactly what I mean.
And it doesn’t require being on foot for it to be so. Las Vegas could literally not be more than a tiny town of desert rats without the water rights on the Colorado they have, same with Phoenix.
Instead they’re huge bustling metropolises.
Even with the issues going on in Europe, crops may die, farmers may go bankrupt - but no one will be literally without water and die from it, or even have to resort to overland tanking.
According to this random PDF from one of the Universities there, the typical household has decreased water usage down to 222 gallons a day. Which is quite low compared to the average in the US, no question.
The current Las Vegas metro population (not counting visitors) is 2.2 million people.
So that’s roughly half a billion gallons of water a day, or 178 billion gallons of water a year. Just for residential, not counting businesses, which typically are much larger water users.
Las Vegas typically gets a bit under 5 inches of precipitation a year.
5 inches of water on an acre of land is equal to 135770 gallons (an ‘acre inch’ x 5).
So to support the current residences in Las Vegas off precipitation alone, they would need to capture 100% of all rain over an area of approximately 1.2 million acres, or 1875 square miles.
Again, that isn’t counting commercial use at all.
Damming up the river which is the final terminus of a watershed estimated at 246,000 square miles (aka the Colorado) makes this a drop in the bucket.
Constructing something equivalent independently?
Not so easy.
And Las Vegas doesn’t have geology amenable to making due with some local damming. Red Rocks is quite pretty and would make a dent, but isn’t big enough.
