Overview 7
duction 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 called Sustainable Water Management Improves Tomorrow’s Cities Health (SWITCH) developed institutional guidelines and piloted a low-cost treatment system to facilitate the safe reuse of wastewater for urban irrigation, while minimizing health risks. Matching water quality to its intended function is the future in many cities, and the present in some. The one source, one system, and one discharge approach assumes that all water should be treated to the drinking water standard regardless of the purpose for which it will be used (human consumption, industrial use, or garden and park watering). This is an inefficient use of money, energy, and water. The concept of water that is fit to a 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. The eThekwini Water Services developed a strategy to recycle wastewater as an additional water source for industrial use. At operational capacity, the reclamation plant meets 7 percent of Durban’s water demand and reduces the wastewater discharge by 10 percent. As a co-benefit, industrial customers reduce their costs by purchasing reclaimed water rather than high-quality, potable water. Wastewater reuse needs to be considered, in particular where water is scarce. If water is scarce, then stormwater, greywater, and even wastewater are potentially economically attractive sources. Windhoek, Namibia, has an annual rainfall of only 350 millimeters, is 750 kilometers from the nearest perennial river, and is a rapidly growing city. Driven by these pressures, 26 percent of Windhoek’s water supply comes from wastewater reuse—a system that has stood the city in good stead for decades. In the Arua case study carried out for this book, analysts propose a low-tech system to treat wastewater in the expanding outskirts of the city. The system would combine decentralized wastewater treatment systems (DEWATS) with soil aquifer treatment (SAT) to treat wastewater that replenishes groundwater, which is then reused for the potable water supply (see Figure 2). One alternative that has been seriously discussed for Arua is to take water from the Nile River, which is 40 kilometers away, and lift it 700 meters to serve the city (Eckart et al., 2012b). An IUWM approach might enable postponing the Nile River plan until the distant future.