ABSTRACT
1.1 INTRODUCTION
An urban population demands great quantities of energy and raw materials, as well as the removal of waste, some of which turns into environmental pollution. Indeed, all key activities of modern cities – transportation, electricity supply, water supply, waste disposal, heating, supply of services, manufacturing, etc. – are characterized by these problems. Thus, concentration of people in urban areas dramatically alters material and energy fluxes in the affected areas, with concomitant changes in landscape, altered fluxes of water, sediment, chemicals and micro-organisms, and increased release of waste heat. These changes then impact on urban ecosystems, including urban waters and their aquatic ecosystems, and result in their degradation. Such circumstances make provision of water services to urban populations highly challenging, particularly in megacities, which are defined as the cities with 10 million or more inhabitants. Yet the number of these megacities keeps growing, particularly in the developing countries, and this further exacerbates both human health and environmental problems. The growth of the number of megacities is illustrated in Table 1.1, listing megacities in 1975 and 2003, and predictions for 2015.
