Because the economics of desalination require locking in long term purchase/production rates at prices that dwarf current and other sources of water.
SD's Poseidon desal is projected at ~$3.7k per acre ft for 2026 whereas SDCWA SWP water is ~$1.5-1.9k acre ft.
Leak fixes, groundwater recharge, local aquifers, water banking, potable reuse, etc. are all more economical means of bolstering water supply.
A big factor in determining desalination placement in the region are the groundwater basins. Limited size and availability makes the case for desalination as means for resiliency. Another is that situating adjacent to power plants so as to use their already coastally degraded intakes/outfalls. Doheny is to use subsurface slant wells for intakes, but it's also lower output too.
As for LA. they're working on getting their potable reuse plants/projects up and running. The largest indirect potable reuse plant in the world has been operating in OC for ~18 years. Lower operating costs than desalination, reduced wastewater discharge, and reduced coastal impact.
A big factor in determining desalination placement in the region are the groundwater basins. Limited size and availability makes the case for desalination as means for resiliency. Another is that situating adjacent to power plants so as to use their already coastally degraded intakes/outfalls. Doheny is to use subsurface slant wells for intakes, but it's also lower output too.
As for LA. they're working on getting their potable reuse plants/projects up and running. The largest indirect potable reuse plant in the world has been operating in OC for ~18 years. Lower operating costs than desalination, reduced wastewater discharge, and reduced coastal impact.