Reuse of greywastewater in multi-story buildings: a sustainable solution to save water

Gray water makes up 60-70% of a home's water requirement and thus can be an alternative source of water for flushing toilets. However, although it is intended to be quite "clean", it can be contaminated and thus pose potential health and aesthetic risks. This article describes the quantity and quality of different sources of domestic gray water and their relative contribution with respect to reuse for toilet flushing. The dishwasher was found to be a major source of organic matter and nutrients, while baths and showers were identified as major sources of fecal coliforms. Six different scenarios were studied, in each of which a different greywater source was xcluded from the ‘mainstream’ greywater stream and the impact on the quality and quantity of the raw ‘mainstream’ was examined. The potential for water savings in the domestic sector was then assessed, with Israel serving as a case study, representing a semi-arid country suffering from water shortages. Reusing greywater for toilet flushing in the domestic sector will increase the sustainable use of water in the urban environment.