Comment by londons_explore

Some older and less efficient desalination plants directly burn oil/coal/gas to desalinate water, so no electricity is involved.

That is perhaps the source of the discrepancy.

With cheap oil, there is little financial incentive to upgrade these plants.

Remember the government need not 'pay' market price for this oil - they can prop the market up by restricting oil exports whilst simultaneously using oil internally at production cost.