An Integrated Perspective for Urban Water Management 53
also be considered. For example, following a decade of work, the new Nairobi Master Plan considered a large range of options, and groundwater was introduced as a major and systematic water source for the first time in Nairobi’s history (Hirji, 2012). By combining the concepts of water fit for purpose and security through diversity, all potential water sources can be modeled to maximize end use and system efficiency. This approach can reduce fresh water use and costs and may improve environmental outcomes (Donkor and Wolde, 2011; GWP, 2010; Sharma and Vairavamoorthy, 2009).2
Box 2.8
Combining Water Fit for Purpose and Security through Diversity: Windhoek, Namibia With annual rainfall of only about 370 millimeters, high surface evaporation rates, and a distance of 750 kilometers to the closest perennial river, Windhoek faces severe challenges in securing its water supply. All potable water resources within a radius of 500 kilometers have been fully exploited. And the city is growing rapidly. Driven by these pressures, Windhoek now relies on four main sources of water: surface water from dams; groundwater from 50 municipal production boreholes; reclaimed water from the New Goreangab Water Reclamation Plant (NGWRP); and reclaimed water from the Old Goreangab Water Reclamation Plant (OGWRP). While the NGWRP reclaimed water contributes to the potable water consumption of the city, the reclaimed water from OGWRP is used to irrigate parks, golf courses, and cemeteries. Windhoek is one of the few systems in the world that recycles treated wastewater for drinking water. Figure B2.8.1 Water Sources for Windhoek, Namibia 6%
Surface water
20%
Groundwater New Goreangab Water Reclamation Plant (NGWRP)
8% 66%
Sources: Lahnsteiner et al., 2007; Van der Merwe, 2000.
Old Goreangab Water Reclamation Plant (OGWRP)