In the average British or American home, as much as 60 percent of total wastewater produced is so-called greywater; that is, wastewater not of drinking quality, but not too heavily polluted with human or animal waste or industrial chemicals (i.e., not “blackwater”). With growing pressures on water supply caused by demographic change (urbanization and the rise in single-person households) and by climate change (which threatens a significant reduction in available freshwater resources for many parts of the globe), there is renewed interest in either reducing greywater production or finding new social and economic uses for it.

Before considering the technological issues attendant on wastewater reduction or reuse, a little historical context is important. Though it may seem entirely natural to us now, the use of large ...