The toxicology potentials ...

The toxicology potentials are NOT even known well, because we can not even know effectively just what toxicant actually exist in a given grey water. If you can't really know WHAT to test for in a sample, and many toxicants do NOT even have analytical protocols developed, how can we in good faith due diligence scientific integrity state whether or not a reuse is 'safe'. There will always be reasonable doubt about the safety. 'Safety', is always relative, but we have existential responsibility to use all available caution in public health best management practices. Clean, freshwater scarcity is an immense pressure to shortcut the whole investigatory aspect of due diligence assessment, this is a very important issue. To be more a part of the solution than a continuing part of the problem for public health responsibility, we must all 'doubt, without unbelief, of the  things to be believed'. We have great responsibility, and tools that are not yet adequate to use, but must always strive for excellence, while fearing we are not really being adequate. Short of reverse osmosis everywhere, we must strive for diligence. IMHO