100 The Future of Water in African Cities
Security and cost effectiveness can be enhanced through diversity and clustering. Arua has a diversity of sources that it can tap, and that might provide sufficient water. These include surface water secured through enhanced watershed protection, groundwater, water reuse through greywater recycling, and (to a limited extent) wastewater reuse. Based on unit costs obtained from NWSC, these solutions are all likely to be more cost effective than using water from the Olewa River (Eckart et al., 2012b). The cost and applicability of the solutions depend on local factors such as whether the city already exists or is expected to be built by 2035, socioeconomic status, groundwater well location, and topography. Eckart et al. (2012b) suggest an approach in which different clusters of Arua implement different solutions (see Figures 4.11 and 4.12). The cluster approach would be more cost effective because the system for each cluster would be designed to meet specific needs. More importantly, the cluster approach is adaptive and can respond to changing conditions in the future with more flexibility than a centralized system. Protection of the existing surface-water resource is a priority. The viability of this integrated solution—and all other solutions except getting water from the Nile—depends on halting and reversing the negative impacts on surface water in the Enyau River from upstream activities. Upstream watershed protection and improvement are multidimensional Figure 4.11 Unit Cost for Staged Development of Use of Sources for IUWM in Arua, Uganda .
2.5
1.0
2.3
2.3
0.8 0.7 0.6
0.2 0.1 0
1
2
Surface water (upgrading Enyau)
3
4
5
6
7
8
Wastewater recycling (through aquifer recharge)
0.3
Groundwater
0.5 0.4
Surface water (existing Enyau)
Unit cost (US$/m3)
0.9
Surface water (dam at Enyau)
9
10
11
12
13
14
Greywater reuse
15
16
17
18
Potential source (1,000 m3/d) Source: World Bank. Note: The ranges of unit costs (vertical lines) are based on the technologies and approaches used. For example, unit costs for greywater recycling and reuse depend on the treatment choices, and groundwater costs depend on borehole drilling costs and pumping costs to elevate the water. For cost assumptions and calculations, see Eckart et al., 2012b. m3 = cubic meters; m3/d = cubic meters per day.