Agreed, especially in water limited areas, but there's a reason it is used. potable water has very well defined properties. Its has a low salt concentration, p

Agreed, especially in water limited areas, but there's a reason it is used. potable water has very well defined properties. Its has a low salt concentration, pretty well known (and diminishing) chloride concentration, and known hardness. It wont give you any surprises when designing a water system. Grey water is whatever a human decided to put down certain drains. This could be very benign, but end users are... special. Will they out cooking grease down the drain? Will they pour industrial cleaners? How about if the end user is an artist who etches glass in the attic bathroom and rinse the HF in the sink? Will they pour "Jimmy"'s, the fish, bowl water and sand? Is shower water "grey"? How about those fellows (they exist) who poop in the shower and squish it down (one of the grossest things I learned on the internet)? And what about "Poochie", the pitbull, who loves to drink from the toilet bowl? What about "Max", the three year old toddler, who loves to wash his hands in the toilet bowl? Grey water should be used, extensively, but it is not a turn-key solution, and it certainly is way more expensive to build for.