The saltwater is in the ocean, and the agricultural areas lacking water (south central valley) are on the other side of the coastal mountain range. So it will be a huge energy expenditure to 1) desalinate and 2) pump the water over the mountain range.

I suspect it would be too expensive for agriculture, which relies on artificially cheap water.

"The saltwater is in the ocean, and the agricultural areas lacking water (south central valley) are on the other side of the coastal mountain range. So it will be a huge energy expenditure to 1) desalinate and 2) pump the water over the mountain range."

I'm not so sure ...

A large amount of municipal/consumer water, from reservoirs, comes down those mountains - and if the coastal users reduced that demand (as they received water, locally, from desal) then that water could either stay in the mountains or be redirected elsewhere - with gravity.

I'm sure there are many different scenarios but I know for certain that there are big reservoirs away from the coast and at (relatively) high elevations ... those could be used differently.

> A large amount of municipal/consumer water, from reservoirs, comes down those mountains - and if the coastal users reduced that demand (as they received water, locally, from desal) then that water could either stay in the mountains or be redirected elsewhere - with gravity.

Given how small of piece of the water pie municipal/household consumption is, that would have little impact on the overall water crisis, but result in a massive increase in energy consumption, which will not primarily come from renewables. Who should pay for that desalination infrastructure and the energy to run them (to say nothing of the externalities of all that extra fossil fuel consumed)?

This just makes me picture big pipelines following (in reverse) the course of the natural watershed... some desal plants off the coast of S.F. or Marin peninsulas with pipes in through the Golden Gate and up the river delta and fanning out towards Sacramento and south to Fresno etc.

If California agriculture is already untenable at 1c a gallon (as per this comment: https://news.ycombinator.com/item?id=31235312) then its probably not going to be very viable to support agriculture with desalination plants.

> At what point should desalination plants be considered for agriculture irrigation in California?

When food becomes expensive enough, and water becomes expensive enough, it will be "economically viable" and done.

I ran the numbers once and you'd have to basically turn the entire coast into desal plants to make enough water for ag. I don't think it's viable, either environmentally or economically.