510 ITU‐T's Technical Reports and Specifications 3.5 Water availability and quality Urban water sources are very diverse. They include rivers, lakes, reservoirs, groundwater, desalination plants or a mixture of these sources. In many metropolitan areas, however, due to the growth of urbanization, the supply may extend far beyond the city's watershed. Such large cities rely heavily on a regional scale supply and distribution system. This is further complicated as freshwater is unevenly distributed over space and time, which places major planning and management challenges to the water sector. Approximately 700 million people in 43 countries are currently suffering from water stress and scarcity15, with over 1 billion people without access to clean water16, and over 2.6 million lacking adequate sanitation facilities17. In developing countries, poor water and sanitation facilities are the source of health problems for almost half of the population, and can be linked to 80% of diseases18. Urban pollution has also gradually led to the deterioration in water quality. Only 10% of the world's cities currently have water treatment facilities, and 90% of untreated wastewater in developing countries is discharged into rivers19, further decreasing the availability of clean water resources for urban inhabitants. Therefore, providing a clean supply of water is considered to be both challenging and expensive. Considering existing gaps in water demand and distribution, climate change impacts and poor water management magnify the vulnerability of countries that are experiencing water stress and weak water infrastructure. Water scarcity is not only a threat to human and economic development, but it may become a source of political instability in years to come. Illustrating the magnitude of water‐related vulnerability at the global level, Figure 4 provides a baseline of water stress and projected changes by 2025. Climate change‐related stressors on the urban water management are explained below.