ITU‐T's Technical Reports and Specifications 503 1 Introduction The Water cycle (water resource, production, distribution, consumption, collection and treatment of waste water) play an integral part of the urban system, influencing each pillar of the urban society and its functionality, sustaining populations, generating energy, supporting tourism and recreational activities, ensuring environmental and human health, and fuelling local economic development. Such increasing convergence fosters urban growth, as more than half of the world's population currently reside in urban areas1. It is estimated that urban populations will increase from 3.6 billion in 2011, to 6.3 billion in 20502. Urban areas will also have the task of absorbing rural populations, as their growth continues to decline. As illustrated in Figure 1, the availability and distribution of water resources is intrinsically linked to the city's operations in areas as diverse as housing, health, economic development, tourism, recreation, transport, waste management and energy. Source: Howe et.al. (2011).3 Figure 1 – Interconnectedness of water and cities The increasing concentration of people, economic activities and assets in urban areas usually generates high amounts of waste and greenhouse gas pollution, heightening the city's susceptibility to the risks posed by disasters/hazards, as well as to the impacts of climate change. Thus, unbridled growth in urban areas poses socio‐economic and environmental challenges to residents, businesses, industries, municipalities and governments alike. As per the focus of this Technical Report, it also poses significant challenges to urban planners in terms of effective and sustainable water management.