The water issues are less due to actual desertification (it's a contributing factor too, of course) and more caused by the ancient and perpetually leaking pipes infrastructure. Way more compromised on the weastern side than on the opposite part.

Speaking with the experience of someone who has spent a good half of his life on that island: Sicily's problems are mainly due to the following factors, in this order: culture and mismanagement. Everything else (yes, including the organized crime) comes in a very, very distant third place.