re: Futuristic wall skyscraper will house 9 million people in Saudi Arabia

Septic? That's part of the problem.
But first, where are the desalinization plants? And the pumps to move that water and to pressurize it, once it's moved. (Not to mention disposal of the salts that are left.)

Speaking of high structures to pressurize the water, where are the minarets? They are going to need them every so often because nobody has the voice to span that.

Back to septic needs: certain folk in that part of the world are accustomed to squat where ever they are when they need to relieve themselves. Will the cleaning crews come around and scrub (pesky water again) after the chosen people have chosen where to go?

Rooms with a view. Of nothing.

I wonder if some of the oil bearing very porous limestones are under this?