Greywater

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 quantities of water for the removal of human wastes has not been with us forever. Indeed, the decision to flush away human waste with water was another Victorian contribution to world civilization. Following the cholera epidemics of the 1850s, politicians and health authorities made the connection between contact with human waste and contaminated drinking water supplies and embarked on a series of major public works that changed the face of London and, subsequently, other world cities. There is, of course, the famous story of Dr. John Snow cutting off a contaminated pump handle in London's Soho, with immediate reductions in cholera infection rates. Slightly later, Chief Engineer of the London Metropolitan Board of Works Joseph Bazalgette responded to crises such as the 1854 cholera outbreak and the “Great Stink” of 1858 to win approval for the construction of more than 1,000 miles of sewers to collect and transport London's “nightsoil” away from London. At about the same time, businessman Thomas Crapper began patenting and marketing indoor water closets for the convenient removal of human waste. The first public toilets had been installed at the Great Exhibition of London in 1851, but the idea caught on rapidly, and by 1900, there were more than 100 in the capital alone.

Together these and other urban innovators of the mid-19th century ushered in a “great sanitary awakening” that saw increasing volumes of water used not just for bodily waste removal but also for greater and greater levels of personal and domestic hygiene. Government authorities across the rapidly industrialized world even hired public health specialists whose job involved educating the poor, urban underclasses about washing their homes and themselves more often and to a higher standard. From this decade forward, human health was to become interlinked with the use of increasing volumes of water for washing bodies, homes, and (more recently) cars, and for removing our bodily wastes.

We have thus reached a situation whereby each and every European is consuming 60–70 liters of water and each and every American 200–250 liters each and every day for uses that do not necessarily make that water unusable for other purposes. It is also undeniable that our use of water for personal and domestic hygiene is grossly inefficient, with the average domestic shower unit consuming approximately 12–15 liters of water per minute—more if a shower pump is fitted. Similarly, modern clothes and dishwashing technologies often do not include water efficiency as a design criterion, consuming as much as 120 liters per cycle. The large differential between European and U.S. water consumption is the subject of continuing controversy, but it seems to be largely related to a higher propensity to have water-intensive sprinklers, high-capacity washing, power washers, and other technologies.

...