Just look at Bermuda. ...
Published by Rodney Ruskin, Geoflow, Inc. - C.E.O.
Just look at Bermuda. See: http://www.eng.warwick.ac.uk/ircsa/abs/1st/184waller.htm and https://images.search.yahoo.com/search/images?p=bermuda+roof+water+collection&fr=tightropetb&imgurl=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2Fb%2Fb0%2FBermuda_roof.jpg%2F800px-Bermuda_roof.jpg#id=1&iurl=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2Fb%2Fb0%2FBermuda_roof.jpg%2F800px-Bermuda_roof.jpg&action=click
It works. Sewage goes into septic tanks and usually is not reused.