[throwaway2037]

First, hat tip on that Guardian article that you shared. The map of desalination plants around the Persian Gulf is excellent.

My first thought looking at it: Why does Saudi Arabia have desal plants in Riyadh? It is 100s of km away from the Persian Gulf! Maybe they want some far away from the Gulf for security reasons? Else, it looks weird. I imagine that they need to pump sea (salty) water from the Gulf to Riyadh, desal it, then pump back the waste water. Quite a journey.