ABSTRACT
Most megacities in Asia are hydrologically negative. Water is made available to them from the reservoirs of nearby major river basins and locally available groundwater. The cities, in turn, generate wastewater that needs to be treated before being released to the nearest river basins and lakes; the lack of treatment of wastewater in cities increases water pollution downstream and thus makes water scarcity worse for towns and cities immediately downstream from megacities. Water scarcity is measured as a ratio of water use to water availability on an annual basis. In order to reduce the water footprint of these cities, water quality and quantity both need to be accounted for. The key to having a sustainable water supply in Delhi – one such megacity that is also the subject under study in this chapter – is to utilize both treated wastewater and harvested rainwater. It is suggested through the case study that water reuse, along with the use of harvested rainwater, must be treated as alternate sources of water for the city. Spatial segregation of the assessment of water scarcity is thus required as different parts of the city have different metrics of groundwater usage and rates of decline in water levels, including the drying up of lakes and a poor quality of water in ponds. A water footprint assessment (WFA) through the quantification of the greywater footprint (I greywater ) and a groundwater scarcity index (I groundwater ) communicates the need to improve the water quality within city limits.
Policies related to water use in regional and city planning which can contribute to reducing the water footprint of megacities are also assessed so that the water quality of nearby rivers (in this case, the Yamuna) may improve subsequently. The reuse of water improves the urban ecosystem and improves the water quality of the river Yamuna, satisfying SDG 6.3 and SDG 6.4, important indicators of sustainable water use. The study shows that for the reuse of water through the proper allocation of recycled water to different sectors, policy thrust and implementation drive are necessary. It is recommended that cities in the future use treated wastewater and restore urban greens to become climate-resilient and sustainable.
