The low hanging fruit have been long picked. Reverse osmosis is within 50% of the thermodynamic limit. If you have gigawatts of low grade waste heat (Iran does

The low hanging fruit have been long picked. Reverse osmosis is within 50% of the thermodynamic limit. If you have gigawatts of low grade waste heat (Iran does, in theory), you can run multistage flash distillers of the waste heat, and those have more than an order of magnitude separation to the thermodynamic limit (they also have lower CAPEX, lower maintenance and lower water pre-treatment requirements than reverse osmosis).