We went through these desalination discussions a decade or so ago in Australia.
Basically, in 99% of the world, you don’t need desal. What you need is to fix up leaky pipes, stop growing rice in deserts and recycle your effluent water.
However, as many people needlessly freak out at the thought of recycled water, you tend to end up with desal plants anyway. Which sit idle most of the time, and will end up running on whatever the local power supply is.
If your normal power is carbon polluting, the desal power consumption will make that problem worse. The hyper-saline discharge tends to make a mess of the local marine environment, too.
