Figure 1.8 Cascading Water Use

to the requirements of the end user. As the quality deteriorates, the resource is directed to uses with lower quality requirements. In this way, water, energy, and materials may achieve two or more functions in sequence. Figure 1.8 illustrates the transition from a once-through fl ow water supply system to an integrated system that matches quality to needs. It cascades water fl ows from drinking and cooking and sanitation to toilet fl ushing and the subsoil irrigation of gardens. The chief benefi t of cascading is effi ciency gains (satisfying many demands with the same unit of supply); however, an added advantage is the capacity to direct scarce resources to essential needs during diffi cult times. Resources may be cascaded through multiple uses and then, through processing, may be looped back to the original point of use. Considered a water-scarce city-state, Singapore adopted an integrated water resource management strategy that includes many integration strategies, including the cascading and looping of water resources (fi gure 1.9). The approach successfully lowered annual water demand in the city from 454 million tons in 2000 to 440 million tons in 2004 (Tortajada 2006), while the city’s population and GDP per capita grew by 3.4 percent and 10.3 percent, respectively. Cascading and looping represented a welcome departure from conventional supplydriven investment approaches (often based on business-as-usual scenarios) to a new resource management approach, including eff ective demand-management control.

Looping resource use: Reclaiming the secondary resource values Looping refers to the closed loop systems that ultimately return water and materials to their points of origin. Returnable drink containers are an obvious example, but the same concept may apply to the much larger fl ows of organic material and water that are carried within drinking containers.

Figure 1.8 Cascading Water Use

Source: Author elaboration (Sebastian Moffatt). Note: As the resource cascades through the system, its quality is matched to the needs of successive uses.