An Integrated Perspective for Urban Water Management 51
Water Should Be Fit for Purpose Supplying water that is fit for purpose—that is, matching water quality to its intended use—will change the requirements of water demand and reduce water abstraction. The application of this principle exposes alternative sources of water that can be safely used for different purposes and can help address the growing gap between water demand and supply caused by the competition for water sources by different users (GWP, 2010; Maheepala et al., 2010; Vairavamoorthy et al., 2008). Some examples of cascading and recycling include greywater reuse for toilet flushing or gardening and nonpotable water for nonprocess industrial demand (Allen et al., 2010; Morel and Diener, 2006; Vairavamoorthy et al., 2009). By avoiding the need for the highest level of treatment for some applications, water can be reused, reducing gross water abstraction and water treatment costs (Foo, 2007; Muller, 2010).
Box 2.6
Cascading Use of Water for Urban Agriculture: Accra, Ghana Irrigated urban vegetable production in Accra provides up to 90 percent of the vegetable needs of the city (Tettey-Lowor, 2009). Most of the agricultural sites are located on valley bottoms along streams and drainage systems and use raw wastewater as the main source for irrigation. The research project SWITCH developed institutional guidelines and piloted a low-cost treatment system to facilitate the safe reuse of wastewater for irrigation while minimizing health risks. A demonstration project was established at the Dzorwulu-Roman Ridge site, which covers an area of 8.3 hectares in Accra. Source: Reymond et al., 2009.
Box 2.7
Water Fit for Industrial Use: Durban, South Africa The concept of water fit for purpose has been implemented in the city of Durban, South Africa, to respond to a conflict between water demand for domestic use and economic development under conditions of water scarcity. (continued on next page)