Is there any place in the developed world that treats mixing sewage into your water source as a viable strategy of providing municipal water?
Las Vegas is a 100% closed loop system. All grey water is recycled back into Lake Mead fur reuse.
Modern sewage treatment is a modern miracle.
That obviously isn't a complete detail of how it works, but what is inaccurate?
Anything that goes down the drain is then treated at a sewage treatment facility and is then dumped into a river/ocean/whatever. Sometimes it’s used for toilet water in large facilities like airports and they put warnings all over everything that it’s not potable because it came from sewage.
There are a few cities with cutting edge “piss to table” technology, but it’s not the norm. The closest you get normally is when an upriver city discharges into a river used downstream.