Urban water systems in large and small cities of India are facing water crises in summers, while monsoons see regular waterlogging. There is a large gap between the water supplied by the city government and the urban water demand in all cities. Sustainable cities of the future will need treated wastewater reuse to be brought into the water allocation framework of the urban water management cycle. This will help in reducing surface water, and groundwater pollution as the treated wastewater from Sewage Treatment Plants (STP) often mix with the raw sewage being disposed of in sewers downstream of STPs, eventually affecting the water quality of surface and groundwater.
The National Water Policy Draft (2012) has mentioned water reuse in urban areas as a measure of demand management; implementation, however, remains a challenge in India. While untreated and partially treated wastewater is being used in the agriculture sector, the health hazards of such use need to be critically assessed. Cities in India still lack 100% sewerage coverage, and consequently, not all sewage reaches treatment plants, thus, while we add more kilometres to the city sewerage network, decentralised treatment technologies are urgently needed to reuse the treated water within the micro catchment of cities.
Reliable reuse of water in cities will address the water scarcity issues, especially in times of drought in semiarid regions of the country; cities like Delhi, Jaipur are a few which will certainly benefit (Melbourne, Australia has benefited through the adoption of water reuse policy). Currently, water scarcity in India is not due to less availability of adequate quantity, but wherever adequate quantity is available, the water quality is poor. Water quality has not been addressed very well in India till date for determining water scarcity. As our grey water footprint increases, the challenge that water quality is posing will only increase.
As the generation of wastewater increases due to the rising population in Indian cities, the grey water footprint will increase, and our precious river basins will get more polluted. Reuse will not only restore urban ecosystems, but it will also reduce pollution in rivers. Currently, at best 50% of the wastewater generated is treated, only about 18,883 MLD (Million Litres Per Day) of wastewater is treated (Central Pollution Control Board (CPCB), 2013), with highest treatment being carried out in Mumbai and Delhi (close to two-thirds of wastewater generated is treated). In the case of Delhi, river Yamuna reports 23 mg/l of BOD to 11mg/l (CPCB, 2015) while compliance is at 3mg/l.
Since the wastewater generated by the city will only increase, it is an uphill task to reduce the effluent, to restore the health of the river, the wastewater reaching the river will have to be reduced. This can be achieved with reuse of treated wastewater near the source; the reuse potential for Delhi is high, like in many other cities. The water demand of Delhi is met with water supplied from the river Yamuna (various canals), river Ganges (through Tehri dam located 320 Km away), as Delhi is rainfall deficit.
The key to having a sustainable water supply in Delhi is to utilise the treated wastewater and rainwater harvesting. With severe depletion in groundwater resources in Delhi and many other cities, restoration of groundwater levels through recharge using rainwater and treated wastewater must be thought of (providing compulsory monitoring facility will be crucial). Besides, there needs to be a water reuse allocation framework and policy thrust and implementation drive.
The current key policy initiatives which support wastewater reuse in urban areas are the Water Act
of 1974, which mandates that urban local bodies must treat wastewater to the required level before discharge, National Urban Sanitation Policy (NUSP), 2008, which recommends a minimum 20% reuse of wastewater in every city. Though reuse is recommended in many policies and programme of the Indian government, there is a gap when it comes to giving clear guidelines and framework to support such an implementation. Extensive use of groundwater for non-potable purposes further
adds to the problem; Delhi is in the overexploited groundwater zone of India.
Some initiatives, like the use of treated wastewater from STP at airports and shopping malls within the toilet facilities of these large buildings across cities, are trying to address the issue. More such initiatives need to be taken by large schools, colleges, railway stations, hotels to bring in large scale water reuse. The water reuse in urban green spaces and city forest area will help in restoring greens and recharge of groundwater. These initiatives need active consideration; the involvement of various stakeholders in cities, amongst them the citizens, are most important to make such initiatives a success.
Currently, India has more than 35 cities with a million-plus population where a detailed water demand assessment is needed, based on which reliable urban wastewater reuse framework and guidelines for reuse at the city level can be implemented. This will turn out to be an essential tool for drought risk management in cities with rainfall deficit, delayed onset of monsoons, and large variability in annual rainfall. We hope that the recently constituted Jal Shakti Ministry will take such initiatives and involve urban local bodies and leading educational institutions to develop implementable decentralised reuse plans.
Beijing and Melbourne have in recent times contributed significantly in leading the way in reuse of non-potable wastewater.