ITU‐T's Technical Reports and Specifications 507 3.1 Rapid urbanization Cities around the world are continuously providing financial and specialized services for businesses, industry, and manufacturing sectors, among others. The emergence of new markets has contributed to a sharp population increase, fostering urbanization. The global urban population is estimated to be 3.5 billion of inhabitants, and is expected to surpass 5 billion by 20306. This rapid growth engulfs outlying towns and blurs rural/urban boundaries creating peri‐urban areas, areas immediately adjoining urban areas that are localized outside formal urban boundaries and urban jurisdictions, and in some regions, urban corridors, city chains and megacities. Megacities and metacities – defined by the UN‐Habitat as cities with more than 10 million inhabitants or 20 million inhabitants respectively – are growing rapidly, particularly in developing countries of Asia, Latin America and Africa7. It is estimated that by 2025 there will be 27 megacities, 21 of which will be located in developing countries. Projections suggest that by 2015, Bombay (22'6 million inhabitants), Dhaka (22'8), Sao Paulo (21'2), Delhi (20'9) and Mexico City (20'4) will be among the six biggest megacities, each surpassing 20 million inhabitants8 (Figure 3). Source: Kraas and Nitschke (2008).9 Figure 3 – Projected megacities, 2015 These highly concentrated populations and the increasing size of cities have posed severe strains in local water resources, as cities are confronted by the need to meet an increasing demand for water resources. In the case of many cities, responding to this high demand has led to unsustainable water usage and over abstraction, and a depletion of groundwater and rivers that has serious consequences on water sources and on the environment. These challenges can have severe effects in megacities located in arid and semi‐arid areas, particularly as climate change impacts further constrain their ability to provide access to a reliable and clean supply of water. The inability to provide citizens with the necessary infrastructure has caused other problems, including the growth of the informal supply of drinking water, wastewater collection and disposal