What is the most pressing challenge facing the Middle East in terms of its water supply?

Well, the middle east countries mostly have deserts and have little drinking water sources as far as I know. For example, United Arab Emirates had the same problem. They would make money from selling their oil but didn't have water. So they had to buy water from elsewhere.
But that was until, they got a solution by using the technology to change sea water into drinkable fresh water. I believe it was the South Koreans who helped them?