One of the barriers to converting wastewater to drinking water is that it still has small quantities of "emerging" pollutants, basically weird stuff that humans make that can't easily be removed. Things like pharmaceuticals, tiny bits of plastic (that research shows may pass through the blood brain barrier."
The only way we are going to be able to handle a growing population in the dry southwest is to reuse and recycle water. We need an efficient and cost-effective way to remove these pollutants. Even if the amounts are parts per billion, they will over time build up if they don't break down.
New German technology referred to as Wasser 3.0 (Water 3.0) is now being test in wastewater treatment plants.