Re: Couldn't they come up with...
Most desal plants are energy intensive, because you've either got flash evaporation, vacuum evaporation, or membrane methods that use high pressure to squeeze water through a membrane leaving the impurities behind. All are very energy intensive, and there's nothing yet that looks to to be a game changer. Relatively low pressure membranes do exist, but there's issues with clogging, durability, and the costs are high.
A more sensible approach is probably to use a thermal evaporator adjacent to a big waste heat source (eg a coal fired or nuclear power station). As an example, Ratcliffe coal plant in the UK generates 2 MWe, and "loses" 11 million tonnes of water through its cooling towers. Not really an issue in the area around Ratcliffe, but that evaporation could be condensed to very clean water in more parched areas of the globe. And that is enough water for around 200,000 people, with the only energy required being the condensation stage. There's the issue of where the water comes from for cooling in the first place, but if you've got an existing thermal plant somebody has had to sort that out already. Seawater cooling for power plants is usually not evaporative, but with suitable measures to rinse the heat exchangers there's no reason why it couldn't be,