Water is heavy to move and process; efforts to make desalination work are energy-intensive. Given the cost of petrol, it may be prohibitive. All this is changing! The cost of solar is dropping fast and the efficiency of the panels is increasing. Given the potential for efficient solar power generation, desalination makes more sense. With Tesla working on large battery storage devices, we may well find a way to significantly supplement our dwindling water supplies.
It would be sensible to start on these developments before the situation has shifted from critical to dire.