In the arid SW of the USA we ...

In the arid SW of the USA we have been using grey water to irrigate golf courses, parks, crops and gardens.  I can't speak to reuse for the home interior but reuse of grey water has been studied quite extensively in the US.  You might want to query the Department of Agriculture for some of the research that has been conducted on this topic.  Much of the DOA work was in conjunction with EPA.  As noted Constructed Wetlands have the ability to remove most contaminants except some pathogens.  We use wetlands to remove heavy metals and have been doing so for 30 years.  www.rmc-ut.com.