Desalination has high capital costs, but the energy usage isn't really a problem at all.

A modern plant uses 2.5-3.5 kWh/m^3 [1]. My household uses something like 9 m^3 per month, so that would be about 27 kWh per month. At PG&E's rather high peak rates, that's $10/month, which is less than the marginal cost of that water. Of course, to the extent that energy costs matter, desalination plants will not use retail power at peak times.

[1] https://www.amtaorg.com/wp-content/uploads/7_MembraneDesalin...