Chapt. 21- Emerging water crisis: Impact of urbanization on water resources and constructed wetlands as a nature-based solution (NbS).

Water is indeed one of the most important matter, providing functionality to life forms and makes this planet habitable. Humans did not imagine their life without water. Ever-growing anthropogenic stress due to extensive urbanization and industrialization leads to the fatal impact of emerging water crisis in today's world. Along with economic shifts, extensive resource-intensive consumptions have increased the freshwater withdrawals for different sectors by six or seven times since 1900s. With less or almost no water recovery after end use from various sources like- wastewater along with unsustainable urbanization makes the situation even worse. Wetlands play a crucial role in regulating the global climate and are natural biofilters for pollutant removal, nutrient absorption, and efficient detoxification of many toxic and harmful chemicals into non-toxic forms. They are considered as one of the most productive ecosystems, acknowledged by the United Nations to achieve SDG-6 (clean water and sanitation). Constructed wetlands based on various physiochemical and biological characteristics of natural one could be used as an alternative in modern urban areas to combat the water crisis. In this chapter, we highlight the ongoing problems related to water scarcity and crisis in temporal and spatial terms, and attempt to put forward the role and importance of natural and constructed wetlands in maintaining a sustainable aqueous environment in urban localities.