Tom, if you google "recycling sewage treatment water", you will see that there are places in the world that treat waste water to the point where it is usable for irrigation and even drinking. Cost as always is an issue, but the math makes more sense as the scarcity worsens.
Realistically, many cities get their water from rivers downstream from where another city dumped their treated water. It is a matter of dilution, filtration and treatment.
I am not suggesting it is easy but plan A isn't working, we better start figuring out plan B. I'd at least be trying to avoid having to deal with that YUCK factor mentioned earlier as long as possible.
There are ways to better allocate the rare and becoming rarer resource of water in a much smarter manner than we have traditionally done in this country in general but especially in the drier parts of the country in particular.
Like another resource we don't manage very well, oil, we bury our head in the sand until a full blown crisis is at hand then face painful consequences that could have been avoided with a little forethought. Collectively, people can be so stupid.