– Xochielt Sanchez
Answer by Robert Frost:
It can be done and it is done. But it isn't done on very large scales because it is currently* very expensive. On average, desalination of sea water costs three times as much (up to $8 per 1000 gallons) as obtaining water from fresh water sources.
The two most common methods used to desalinate water are multistage flash distillation, which uses heat to evaporate water (the steam is then separated from the salt and recondensed into fresh water), and reverse osmosis desalination, which pumps water through membranes that filter it.
That means the choice is to rack up a huge energy bill boiling water or a large energy bill pumping and a huge equipment and maintenance bill.
Desalination is becoming more common in desert areas like the Middle East. Israel now gets 40% of its water via desalination and the world's largest desalination plant is in the UAE.
*The technology is advancing. Lockheed is prototyping graphene filters that are more durable and effective.