It's not that we can't remove the salt, it's that electrolysis to remove salt from the water is very expensive from an energy perspective, which makes it expensive from an economic perspective too. A massive spike in the price of water would cause a widespread crisis impacting every corner of the economy.
Also, building out the infrastructure required to do electrolysis on that scale would take a lot of time and resources on its own.
Strawman rolled a nat 20 on its DEX save, takes no damage sorry