In-Depth Analysis of Water Management Challenges in Selected Cities 87
water. It should be noted that stormwater and greywater are not used directly for household use, but either used for nonpotable uses or recharging of groundwater (Eckart et al., 2012). The IUWM options provide more resilience to unexpected outcomes. Figures 4.2 and 4.3 illustrate how consideration of additional sources of water may allow postponement of some water supply infrastructure. Alternatively, those same sources could function as a buffer against higher demand and/or lower water supply than anticipated in the planning forecast for the Feasibility Study and Master Plan for Nairobi (AWSB, 2012). By modeling the urban water cycle as one system, we find that solutions are available to address the water gap in Nairobi at reasonable cost. Cost schedules were developed for a wide variety of water sources (see Annex 2 of Eckart et al., 2012). These illustrate a large variation in costs depending on specific circumstances, for example, whether solutions are implemented at household or at cluster level. As an illustration, we provide the cost calculation for the staged development, IUWM scenario 2; see Figure 4.4 (Eckart et al., 2012). Figure 4.4 Water Resources and Unit Costs for One Alternative IUWM Solution 1.7
1.2
2.5
2.3
0.8
0.2
Water demand management
Existing water resources
Leakage management
Conventional water resources (new)
20 60 10 0 14 0 18 0 22 0 26 0 30 0 34 0 38 0 42 0 46 0 50 0 54 0 58 0 62 0 66 0 70 0 74 0 78 0 82 0 86 0 90 0 94 0 98 1,0 0 2 1,0 0 60 1,1 00 1,1 40 1,1 8 1,2 0 20
0
Greywater reuse (cluster)
0.4
Private boreholes
0.6
Stormwater (cluster)
Unit cost (US$/m3)
1.0
Potential source (103 m3/d) Source: World Bank. Note: The range of unit costs (vertical lines) are based on the technologies and approaches used. For example, unit costs for water demand management depend on the quality and type of water saving devices; leakage management costs depend on the cost of water production and leakage control strategies; greywater costs depend on the treatment choices; stormwater costs depend on whether structural and/or nonstructural measures are applied; rainwater harvesting costs depend on whether simple storage tanks or pumping to elevated reservoirs are required. For cost assumptions and calculations, see Eckart et al., 2012. 103 m3/d = 1,000 cubic meters per day.