[kortilla]

In the vast majority of developed nation cities, drinking water comes from reservoirs and goes through whatever treatment is required to make it potable.

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.