Desalinization is not an option, because farmers would have to pay market prices for new sources of water, and desalinized water would be unaffordable for agriculture. If you needed water for drinking, or for flushing toilets, then desal is an option.
But as has been mentioned many times, 80% of the water in California goes to agriculture. And the farmers who use the bulk of that water pay ludicriously low prices for their water. You can grow rice in the desert if you pay $2 an acre-foot for water, but not if you have to pay $2000 an acre-foot. You’re never going to have desal water as cheap as water from the mountains.
This is why worrying that people will have to leave California are silly. There’s plenty of water for everyone to drink, flush their toilets, wash their dishes, fill their swimming pools. Maybe you’ll have to forgo watering the lawn, so what, put down some crushed gravel and a cactus, you live in a desert.
That is, there’s plenty of water for home use, except farmers get first crack at the water, and the cities have to scramble for the dregs. Cities might have to go with desal, not because there’s not enough water, not because they can’t pay for the other water, but because every drop is taken by agriculture. Cities can make residents pay market price for household water, but somehow the state can’t make farmers pay market prices for agricultural water.
So bottom line, California is not getting any new sources of water. Not going to happen. No, we’re not diverting the Mississippi River over the Rocky Mountains so California farmers can dump it on their fields. No we’re not diverting the Great Lakes, or the Columbia River, or the Yukon River. And no, we’re not desalinating water for California farmers, because they’d spit on water that costs that much. They don’t want water, they want cheap water. Big difference.
Of course there’s no incentive for an individual farmer in California to conserve water, or switch to dryland crops. He’s got a certain amount of free water that he can’t sell or give away, it would be crazy for him not to use it.
California is going through a drought, which is bad. But California isn’t having a water crisis, it’s having a water management crisis.