Not Phoenix so much. California (and Nevada) is where they're desperate for potable water, even though the Pacific Ocean is right there waiting to be de-salinated.
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Idea: re-engineer the water supply system for dual water supply, in California and Nevada, so that every time a toilet is flushed, only non-potable Pacific Ocean sea water would be used to flush the toilet. Maybe also for public display fountains in Las Vegas, spray washing parking lots, etc.
A separately kept potable water supply could thereby be better conserved and made more available for such uses as bathing, dishwashers, clothes washers, drinking water, etc.