54 The Future of Water in African Cities
Urban Groundwater: Sustaining Water Security and Increasing Water Treatment Potential For some cities, groundwater represents a strategic resource to sustain baseline water supply for their population. It can also be used to maintain water demand during drought or to increase security of supply affected by reduced river flow. Given the expected urban population growth rates and in view of some climate change scenarios, groundwater expansion is considered as one of the preferred responses in areas of Africa where suitable aquifers are present (Foster et al., 2010b). Urban water management can make use of the hydrogeological characteristics of groundwater to improve water supply. Aquifers have the potential to be used as seasonal water storage through groundwater recharge processes and water reuse schemes, which sometimes incorporate this type of solution. Different types of aquifer recharge techniques allow the infiltration of treated sewage effluent to facilitate nutrient and pathogen removal. The recovery of such water after pumping enables its use for water supply purposes after treatment (Dillon et al., 2009). Groundwater abstraction in urban areas is generally done with little conjunctive use of surface and groundwater (Foster et al., 2006). In rapidly expanding cities, conjunctive use of surface water, groundwater storage, and abstraction can complement urban water supply and add security and flexibility in case of seasonal resource variation. Coordinating management responsibilities that are currently divided between local and national administrations, and informing practitioners of the benefits of rational, conjunctive surface-groundwater development, can improve resource use and delivery of urban water services (Foster et al., 2010a). Groundwater abstraction in cities in Africa tends to be informally organized. In Sub-Saharan Africa only a few large urban water utilities— for example, Abidjan, Bamako, Dodoma, and Lusaka—use groundwater as a permanent source of supply (Foster et al., 2010b). However, privately owned boreholes and wells for direct water collection (or reticulation to standposts) have widely become the fastest growing source of urban water. According to some estimates, 24 percent of urban water supply is collected from waterwells, which represent the fastest growing source and serve an additional 1.5 percent per year of the urban population (Tuinhof and Heederik, 2003). In some areas that lack or have a poor municipal water supply and/or high water prices, groundwater is privately abstracted, resulting in a mushrooming of private in situ well construction. Enforcement of regulation of private wells in urban areas is