Desal can be used for backup when needed—it would then be more expensive when used but it is a lot better than running out of water.
As I pointed out desal at least the way Israelis do it cheaper than muni water is here in North Texas. $1.96 for desal vs $4.5 for the same 1000 gallons. We are too far from the Gulf to use desal directly but pipeline transport of water is not that expensive as long as it’s under 1000km and not up 2000+ meters of elevation. Neither would apply for North Texas we are 560km from the Gulf and only at 300 meters above MSL. The better choice would be to pay for desal water for Houston on the Gulf Coast and then take the equal amount out of the Trinity River system which today must flow down hill to Houston’s lake Livingston water source.
L.A. And San Diego should both be using Israeli tech directly on the Pacific. Phoenix, las Vegas, and Tucson should pay for the plants and the water for L.A. And San Diego then withhold an equal amount of water upstream in Lake mead for their own use in a one for one acre foot trade that keeps you from having to pump water up hill over the coastal mountains and then again over the Sierra Nevada mountains.
The economic will likely never work for the crops and flood irrigation, nor will it work in dry arid climate with ET values above 30 inches per year or more. There is a fundamental minimum in energy to Desal a cubic meter not even counting O&M for the equipment or capital depreciation plus interest. All of which add to the per unit cost.
“The theoretical absolute minimum amount of energy required by natural osmosis to desalinate average seawater is approximately 1 kilowatt-hour per cubic meter (kwh/m3) of water produced, or 3.8 kilowatt-hours per thousand gallons (kwh/kgal).”
The very best RO eff is double the minimum or 6.5 kWh per 1000 gal there’s 325800 gallons in an acrefoot. You will need 2100+ kWh per acre foot that’s an enormous amount of electricity now factor in to replace the 7 million plus acre feet that agriculture uses per year you get the idea of the power requirements. Put this way every acrefoot needs 2.1 megawatt hours of electricity and you would need 14+ million megawatt hours to replace Colorado river water not even touching the pumping power requirements. California shut down the only power source that has the steady 24/7/365 wattage to even come close to that amount of electricity the Diablo Canyon nuke plant. A 1350 MW reactor running flat out 100% for a year would make only 11,826,000 megawatt hours of electricity so you need two of them just to run RO process then you have to pump all that water uphill over the coastal mountains to the imperial valley and also the central valley farm lands. Deal is never going to replace what the sun does for free with evaporation on the oceans and precipitation over land the amounts of energy in that water that falls from the sky for free is mind boggling. California needs to.learn to live within its water means it’s that simple. The coastal areas can and.should supplement natural water cycle water with Desal but it will never replace Colorado River water on an agriculture scale.