Abstract
This study investigated the new routes of groundwater replenishment in water-constrained urban communities. Against the present water demand of 1,440 million gallons per day (MGD) in Delhi, 1,000 MGD including 140 MGD groundwater is being supplied. Additionally, residents, institutions and commercial occupants are illegally extracting 250 MGD. This groundwater extraction is enormous in comparison with the water injected into the ground through rain water harvesting, resulting in the tremendous depletion of the groundwater table. The aim of the study is to replenish groundwater with tertiary treated effluent available round the year. The study is conducted on one natural water body rejuvenated in the South and another artificial water body constructed in West Delhi with the objective of determining whether groundwater can be replenished with tertiary treated water with an improved quality, and whether it can be replicated elsewhere. The qualities of the groundwater and water tables were checked before and after rejuvenating the water bodies. The utilization of tertiary treated effluents has resulted in raising the groundwater tables from 5 to 7 m and improved the quality of the groundwater in the past 2 years. This practice can be replicated elsewhere as done in Brisbane (Australia) and Singapore.
HIGHLIGHTS
Utilize recycled water for replenishment of groundwater in overexploited water zones.
Treated effluent passes through floating wetlands, surface aerators and filtration.
Water table increased by 7.0 m at Pappankalan and 5 m at Rajokari.
Water bodies becoming the place of recreation for surrounding localities.
These practices can be applied anywhere in India and abroad effectively.
INTRODUCTION
Groundwater is the major freshwater resource that meets around 33% of the global drinking water demand (Li 2016). Most of the water and irrigation demand in India is met from groundwater. Even in the United States, 40% domestic water supply is supplemented through groundwater. Hence, irrespective of whether a country is undeveloped, developed, or developing, groundwater plays a very important role in fulfilling basic needs (Swain et al. 2022). During the last three decades, groundwater exploitation has increased manifold in India due to the growing population and the limited surface water, which has resulted in unexpected groundwater depletion and water quality deterioration, subsequently reducing future water resources for the next generation. This requires a paradigm shift in water policy to recharge groundwater with recycled water that is available round the year (Gdoura et al. 2015) and has many advantages, i.e., reducing the disposal of wastewater in rivers and drains, reducing floods, increasing groundwater levels, and establishing water storages for emergency use (Bouwer 1991, 1996). Moreover, recycled water is used to recharge groundwater all over the world (Ghayoumian et al. 2005). In the United States as well recycled water is widely used for groundwater recharge as supported by the Environmental Protection Agency (Schmidt et al. 2013). This is despite the fact that using recycled water to recharge aquifers invites many controversies, which are largely the result of human mental blocks (Nijhawan et al. 2013). The groundwater recharge through the natural process/filtration is far slower than the exploitation of groundwater resulting in the faster depletion of water tables. Hence, Managed Aquifer Recharge (MAR) has become increasingly important (Asano & Cotruvo 2004; Hochstrat et al. 2010). In Delhi, more than 400 MGD groundwater is being extracted to supplement the gap between drinking water demand and its supply, resulting in a tremendous drop down in the groundwater table in 9 out of the 11 districts in Delhi. However, the efforts for replenishment of groundwater are not enough. Delhi Government incentivises its customers by reducing water charges by 5% for the installation of Rain Water Harvesting at their premises and 15% if their Sewage Treatment Plant, in addition to Rain Water Harvesting system, is functioning (Delhi Jal Board 2023). Despite this incentive, the consumers' response is very poor.
Current status of static water bodies in the NCT of Delhi (Delhi Parks and Gardens Society 2023)
S. No. . | District . | Total Nos. of water bodies . | Non traceable Water bodies . | Water polluted bodies . | Encroached water bodies . | Water bodies converted into Park . | Water bodies near Yamuna . | Maintaining agencies . | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
DDA . | DJB . | BDO/Rev . | MCD . | Ors . | ||||||||
1. | East | 52 | 3 | 16 | 3 | 8 | 17 | 46 | 2 | – | 2 | 2 |
2. | North East | 31 | 2 | 1 | 2 | 8 | 17 | 23 | 2 | 4 | – | 2 |
3. | Shahdara | 23 | – | – | – | – | – | 21 | – | – | 2 | – |
4. | North | 165 | 5 | 14 | 50 | 7 | 21 | 131 | – | 27 | 3 | 4 |
5. | North West | 164 | 1 | 14 | 28 | 21 | 1 | 143 | 1 | 14 | 2 | 4 |
6. | South | 142 | 5 | 11 | 29 | 13 | 2 | 98 | – | 6 | 3 | 35 |
7. | South East | 42 | 9 | 1 | 2 | 2 | 10 | 40 | – | – | – | 2 |
8. | South West | 273 | 6 | 30 | 37 | 13 | 0 | 184 | 1 | 78 | 7 | 3 |
9. | West | 64 | 4 | 16 | 18 | 9 | 4 | 63 | – | – | – | 1 |
10. | New Delhi | 60 | 3 | 3 | 8 | 5 | 1 | 53 | – | – | 3 | 4 |
11. | Central | 29 | 2 | 4 | 3 | 3 | 3 | 20 | – | 1 | 1 | 7 |
Total | 1,045 | 40 | 110 | 180 | 89 | 76 | 822 | 6 | 130 | 23 | 64 |
S. No. . | District . | Total Nos. of water bodies . | Non traceable Water bodies . | Water polluted bodies . | Encroached water bodies . | Water bodies converted into Park . | Water bodies near Yamuna . | Maintaining agencies . | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
DDA . | DJB . | BDO/Rev . | MCD . | Ors . | ||||||||
1. | East | 52 | 3 | 16 | 3 | 8 | 17 | 46 | 2 | – | 2 | 2 |
2. | North East | 31 | 2 | 1 | 2 | 8 | 17 | 23 | 2 | 4 | – | 2 |
3. | Shahdara | 23 | – | – | – | – | – | 21 | – | – | 2 | – |
4. | North | 165 | 5 | 14 | 50 | 7 | 21 | 131 | – | 27 | 3 | 4 |
5. | North West | 164 | 1 | 14 | 28 | 21 | 1 | 143 | 1 | 14 | 2 | 4 |
6. | South | 142 | 5 | 11 | 29 | 13 | 2 | 98 | – | 6 | 3 | 35 |
7. | South East | 42 | 9 | 1 | 2 | 2 | 10 | 40 | – | – | – | 2 |
8. | South West | 273 | 6 | 30 | 37 | 13 | 0 | 184 | 1 | 78 | 7 | 3 |
9. | West | 64 | 4 | 16 | 18 | 9 | 4 | 63 | – | – | – | 1 |
10. | New Delhi | 60 | 3 | 3 | 8 | 5 | 1 | 53 | – | – | 3 | 4 |
11. | Central | 29 | 2 | 4 | 3 | 3 | 3 | 20 | – | 1 | 1 | 7 |
Total | 1,045 | 40 | 110 | 180 | 89 | 76 | 822 | 6 | 130 | 23 | 64 |
Study on current status of water bodies
Water bodies, being one of the important water resources, must have water at least of bathing standard (Supplementary material, Table S1). These must have a natural catchment to catch the rainwater during rains. But, due to the fast urbanization and neglected wastewater management, most of the water bodies in Delhi are heavily encroached upon, consequently shrinking the original catchment area and polluting it. The stormwater surface run-off goes back to roads/colonies resulting into water logging, as no water shed management and no well-defined catchment areas of water bodies exist (Brindha & Schneider 2019). The water in the water bodies is highly polluted because of the dumping of solid waste and the inflow of wastewater and industrial effluent (Supplementary material, Figure S1(a)) into these water bodies. Open drains carrying black and gray waters also face anthropogenic activities causing a high risk of infection and communicable diseases. In this regard, microbiology parameters like Escherichia coliform, total coliform, and total aerobic count are important to be investigated and treated suitably before the treated water is collected in water bodies (Giannakis et al. 2015; Liang et al. 2019; Sharma et al. 2020; Yin & Shang 2020; Krishnan et al. 2021; Yacouba et al. 2021; Bahadur et al. 2023).
The residents nearby and passers-by try to keep themselves aloof due to the bad smell resulted from anaerobic reaction in biomass and the dirtiness in and around the water bodies. However, these water bodies would have been very good recreational places. The polluted water collected in the water bodies percolates into the ground and pollutes the groundwater, which becomes irreparable in the long run, thus reducing further the groundwater resource (Jonah & Dawda 2014). The people using this groundwater through tube wells or hand pumps suffer from waterborne diseases when they draw water from the ground and use for their consumption. The flora and fauna that should have been in natural lakes have disappeared. The birds are flying away from these water bodies instead of toward them. However, thousands of migratory birds as well as aquatic lives can be seen in the rejuvenated lakes or Biodiversity Parks developed by some of the relevant agencies (Supplementary material, Figure S1(b)).
The encroachment of the watershed areas of most of the water bodies has resulted in the accumulation of rainwater in and around the colonies instead of its flowing into the water bodies. Since these slums cropped up in the watershed areas of the water bodies illegally, the government could not provide basic amenities like water and sewerage. Hence, the sewage generated by those residents also discharges into these water bodies through point and non-point sources. The solid waste generated in such slum colonies that have illegally grown in the watersheds of the water bodies is not properly managed. The residents, therefore, throw their solid waste into the nearby water bodies, polluting the freshwater available in these water bodies. The water bodies are generally neglected in metro cities, resulting in their poor maintenance. The residents nearby who are the immediate beneficiaries are also not made aware of the benefits and importance of the proper maintenance of the water bodies. Instead, they consider the water bodies as dumping places for solid waste and sewage disposal.
METHODOLOGY FOR REJUVENATION OF WATER BODIES
Restoration of original and natural watershed of water bodies
Wastewater and solid waste management
All the intakes of the wastewater are identified and marked on the plan. The quality parameters of the wastewater are tested for designing the treatment plant that may deliver the desired quality of treated effluent. The water quality of the water body is intrinsically linked to the quality of the inlets. It is, therefore, essential to trap and clean these before they drain into the water body. A constructed wetland is an appropriate and sustainable solution for this. The natural water treatment arrangements such as wetland systems, soil, filter media, organisms, and so on are used to treat municipal or industrial wastewater, stormwater run-off, and so on. Some of the species of plants used for root zone treatment in a wetland system are Eleocharis palustris, soft stem burus, sweet flag, Narrow leaf cattail, Broad leaf arrowhead, Green Ash, Red Maple, Green arrow arum, and Spartina altemiflora. The constructed wetlands of an appropriate capacity should be planned for the site and integrated as part of the larger landscape scheme, as it involves almost zero operational cost and merges with the overall landscape (Simon & Joshi 2021).
A large amount of solid waste is thrown by the residents in and on the banks of drains, rivers, and ponds. In Delhi, the solid waste generation was estimated to be 17,000–25,000 tonnes/day for the anticipated population of 22.4 million by 2021. Despite efforts to decompose the waste by composting, incineration, and so on, a minimum residue of 4,000–5,000 tonnes/day, i.e., 20%, will require a large area of landfills (MoEF GOI 2001). Hence, there will be a lot of pressure on the municipal bodies to manage even the residue of municipal waste in the future. Without an adequate solid waste management infrastructure in Delhi and better awareness programs, the residents will continue throwing their domestic waste in nearby water bodies, i.e., drains and rivers, ultimately increasing pollution in the water bodies. For preventing the dumping of solid waste into water bodies, the concerned municipality must construct proper Dalao (intermediate large dust bin for collecting solid waste temporarily before disposing at sanitary landfills), and place dust bins at regular intervals for the collection of solid waste. Door-to-door collection of solid waste can be implemented in the surrounding areas of a water body so that solid waste is collected and disposed of properly instead of being dumped in the water body.
The wastewater flowing into water bodies carries a lot of sludge that gets deposited on the bed of the water body besides the solid waste dumped by the residents. The organic matter deposited in the beds of the water bodies gets digested due to anaerobic reaction and generates obnoxious gases, i.e., carbon monoxide, methane, and hydrogen sulfide. To prevent such a situation and ensure clean water in water bodies, it is essential to dredge the historical sludge from the beds of water bodies at regular intervals.
Landscaping of catchment of water body and ecological restoration
The major catchment of a water body must be designed as a wetland park with urban wilderness, attracting butterflies, useful insects, birds, aquatic life, and so on. These wetland parks must be designed to manage stormwater effectively as an integrated part of the landscape. The gardens will also provide high-quality public open spaces for the surrounding communities. These will be pesticide- and herbicide-free zones. This approach would not only enhance the capacity for retention during monsoons but also help reduce pollution load further, increase groundwater recharge, reduce water temperature (as high temperature are unsuitable for certain aquatic life) in extreme summers, enhance the local ecosystems and biodiversity, provide a robust amenity space for the surrounding communities, and facilitate other social needs. Every project of water body restoration will have certain specific site-based requirements that will need to be addressed on a case-by-case basis. In tandem, degraded ecosystems and habitats must be restored where applicable and/or new ecological landscapes created. The natural process of self-revival of water bodies, i.e., wetland systems and ecosystems, must be ensured while rejuvenating water bodies (Mahapatra & Varghese 2017).
Enhancement of socioeconomic values through community participation
Clean water bodies and restored ecologies and landscapes provide the basis for creating public assets in a city in the form of public spaces, recreational amenities, and enhanced biodiversity. These assets must be incorporated in all restoration initiatives to enable the creation of water-oriented amenities that are robust in the long term, giving rise to new zones of growth and opportunities. The most important component of the rejuvenation process of water bodies is the proper maintenance, which is possible with the help of community participation during the planning, construction, and any decision-making, and thereafter in the maintenance and monitoring mechanism so that the beneficiaries may feel the ownership of the project and keep the water bodies in proper condition. The community, which is the beneficiary in the future, can prevent encroachments on the watershed, convince residents not to dump solid waste, and keep monitoring for the proper maintenance of the water body. There are many success stories of community participation in water management in India, i.e., Bangalore Lake management.
Future management standard and monitoring mechanism
The species of plants to further clean treated water are planted near the water body and remaining parts of the residences nearby as mentioned in various studies (Ervin et al. 2006; Pollock et al. 1998; Olde Venterink et al. 2003). The flora and fauna are selected according to the quality of water in the water body and to further the maintenance of the quality of water (Chiarawatchai et al. 2008). The proper maintenance of treatment plants, stormwater drains, plants, and shrubs is to be done per the aforementioned Standard Operating Practices. Table 2 summarizes the key aspects of the maintenance and management of water bodies and surrounding parks.
Key aspects of maintenance and management of water bodies and surrounding parks
S. No. . | Elements . | Details . |
---|---|---|
1. | Active monitoring of water quality | Water quality of the water body and that of the constructed wetland outlet shall be tested weekly. These tests must be carried out by labs certified by the National Accreditation Board for Testing and Calibration Laboratories (NABL) |
2. | Solid waste management | Litter and solid waste including leaves, rubbish, paper, bottles, cans, rocks, and gravel shall be removed from all areas on a daily basis. All refuse resulting from the maintenance operation shall be disposed of at locations designated by the Municipal Corporation of Delhi (MCD). All hardscape areas shall be swept or blown free of debris daily. Construction and demolition daste dumping shall be controlled. |
3. | Constructed wetland management | • Survey to identify new inlets shall be carried out bi-annually and necessary trapping into the constructed wetland should be undertaken immediately. • Need for replantation shall be assessed in 3 months, and then bi-annually thereafter, with replantation carried out as required. • Cleaning of collection cum sedimentation chamber shall be undertaken once every 4 months. • Need for de-silting shall be assessed bi-annually and de-silting shall be carried out as required (usually once in 2–3 years). • Pruning of overgrown plants from Phytorid Beds shall be carried out on a quarterly basis. • Hydraulic water level checks shall be undertaken bi-annually, and action shall be undertaken as required. • Gravel check of Phytorid Beds and reshuffle shall be undertaken bi-annually. • Routine Pump Maintenance shall be undertaken on a quarterly basis. Bioremediation augmentation by Bio-media application in Phytorid Beds shall be undertaken annually. |
4. | Maintenance of landscaped areas | The nature of landscape maintenance should be aligned with the concept of the park. To sustain the quality and health of a wetland garden with urban wilderness, minimal maintenance is required. The following is to be adhered to: • The wetland garden will be a pesticide/herbicide-free zone with only the use of organic manure if necessary. • Pruning of trees, shrubs, ground cover is to be avoided unless carried out to (a) eliminate disease and (b) to keep a 1.5 m zone along pathways free of any obstruction that may cause accident. • Turf areas/Meadows designed as gathering spaces may be mowed if necessary during the growing season to maintain easy access and continued use. |
5. | Irrigation | The irrigation shall be operated at an appropriate seasonal schedule, using the least amount of water necessary to maintain the growth, health, and vigour of all landscape plant materials. All necessary actions will be taken to maintain and repair all irrigation systems on the property. |
6. | Lighting | Lighting fixtures/systems shall be maintained to ensure peak performance during the life of the project. All fixtures shall be cleaned per requirements specified in the project contract. Replacements of fixtures shall be made to remedy breakage and to maintain appropriate lighting levels. |
7. | Replanting and extra work | Plant material that dies through the fault or neglect of the contractor, or because of preventable circumstances, shall be replaced with a specimen of the same species and of equal or similar size as the plant lost. |
S. No. . | Elements . | Details . |
---|---|---|
1. | Active monitoring of water quality | Water quality of the water body and that of the constructed wetland outlet shall be tested weekly. These tests must be carried out by labs certified by the National Accreditation Board for Testing and Calibration Laboratories (NABL) |
2. | Solid waste management | Litter and solid waste including leaves, rubbish, paper, bottles, cans, rocks, and gravel shall be removed from all areas on a daily basis. All refuse resulting from the maintenance operation shall be disposed of at locations designated by the Municipal Corporation of Delhi (MCD). All hardscape areas shall be swept or blown free of debris daily. Construction and demolition daste dumping shall be controlled. |
3. | Constructed wetland management | • Survey to identify new inlets shall be carried out bi-annually and necessary trapping into the constructed wetland should be undertaken immediately. • Need for replantation shall be assessed in 3 months, and then bi-annually thereafter, with replantation carried out as required. • Cleaning of collection cum sedimentation chamber shall be undertaken once every 4 months. • Need for de-silting shall be assessed bi-annually and de-silting shall be carried out as required (usually once in 2–3 years). • Pruning of overgrown plants from Phytorid Beds shall be carried out on a quarterly basis. • Hydraulic water level checks shall be undertaken bi-annually, and action shall be undertaken as required. • Gravel check of Phytorid Beds and reshuffle shall be undertaken bi-annually. • Routine Pump Maintenance shall be undertaken on a quarterly basis. Bioremediation augmentation by Bio-media application in Phytorid Beds shall be undertaken annually. |
4. | Maintenance of landscaped areas | The nature of landscape maintenance should be aligned with the concept of the park. To sustain the quality and health of a wetland garden with urban wilderness, minimal maintenance is required. The following is to be adhered to: • The wetland garden will be a pesticide/herbicide-free zone with only the use of organic manure if necessary. • Pruning of trees, shrubs, ground cover is to be avoided unless carried out to (a) eliminate disease and (b) to keep a 1.5 m zone along pathways free of any obstruction that may cause accident. • Turf areas/Meadows designed as gathering spaces may be mowed if necessary during the growing season to maintain easy access and continued use. |
5. | Irrigation | The irrigation shall be operated at an appropriate seasonal schedule, using the least amount of water necessary to maintain the growth, health, and vigour of all landscape plant materials. All necessary actions will be taken to maintain and repair all irrigation systems on the property. |
6. | Lighting | Lighting fixtures/systems shall be maintained to ensure peak performance during the life of the project. All fixtures shall be cleaned per requirements specified in the project contract. Replacements of fixtures shall be made to remedy breakage and to maintain appropriate lighting levels. |
7. | Replanting and extra work | Plant material that dies through the fault or neglect of the contractor, or because of preventable circumstances, shall be replaced with a specimen of the same species and of equal or similar size as the plant lost. |
NOTABLE CASE STUDIES OF REJUVENATION OF NATURAL AND ARTIFICIAL WATER BODIES
Pappankalan artificial water body
Groundwater quality before and after the construction of the artificial lake at Pappankalan
S. No. . | Parameters . | Before C/O lake . | After C/O lake . | Remarks BIS: 10500 (2012) . |
---|---|---|---|---|
1. | pH | 8.19 | 8.00 | 6.5–8.5 |
2. | Electrical Conductivity | 2,472 | 2,100 | |
3. | Ca | 38.16 | 28.18 | 75 |
4. | Mg | 64.37 | 45.40 | 30 |
5. | Na | 424 | 315 | 20 |
6. | K | 10 | 5 | 10 |
7. | Cl | 424.14 | 315.10 | 250 |
8. | NO3 | 83.80 | 85.00 | 45 |
9. | F | 1.94 | 1.65 | 1 |
10. | SO4 | 37 | 31 | 150 |
11. | NO2 | 0.06 | 0.05 | |
12. | PO4 | 0.05 | 0.05 | |
13. | HCO3 | 372.55 | 285.45 | 244 |
14. | WQI | 215 | — | 200–300 (very poor) |
S. No. . | Parameters . | Before C/O lake . | After C/O lake . | Remarks BIS: 10500 (2012) . |
---|---|---|---|---|
1. | pH | 8.19 | 8.00 | 6.5–8.5 |
2. | Electrical Conductivity | 2,472 | 2,100 | |
3. | Ca | 38.16 | 28.18 | 75 |
4. | Mg | 64.37 | 45.40 | 30 |
5. | Na | 424 | 315 | 20 |
6. | K | 10 | 5 | 10 |
7. | Cl | 424.14 | 315.10 | 250 |
8. | NO3 | 83.80 | 85.00 | 45 |
9. | F | 1.94 | 1.65 | 1 |
10. | SO4 | 37 | 31 | 150 |
11. | NO2 | 0.06 | 0.05 | |
12. | PO4 | 0.05 | 0.05 | |
13. | HCO3 | 372.55 | 285.45 | 244 |
14. | WQI | 215 | — | 200–300 (very poor) |
Floating wetlands and aerators in the artificial water body at Pappankalan STP.
Rejuvenation of Rajokari natural water body
DISCUSSION
The guidelines on replenishment of groundwater were published and welcomed in Australia. These were implemented in the three states, i.e., South Australia, Western Australia, and Victoria. In other states implementation was not progressing, despite the requirement, opportunities, and viability there. These guidelines were reviewed in the last 10 years and risk assessment was also carried out in terms of the quality of waste treatment, soil profiles, and quality of groundwater after its replenishment (Dillon et al. 2020). A similar review of the guidelines and the monitoring of the quality of the recycled water and the quality of the replenished groundwater is also essential in Delhi to ensure the improved quality of groundwater in a sustainable manner.
Although proactive measures are required to be taken to preserve these water bodies not only in Delhi but across the country, these require very harsh regulations and enforcement of the environment law, which are somehow missing. The existing laws related to water bodies can include the polluter pays principle, which must be stringently implemented. These regulations should not be confined to Delhi, but put into action in the whole country without further delay (Kumar et al. 2022). According to the report published by Delhi Parks and Gardens Society, most of the ponds in Delhi have been reduced in the area due to encroachment, siltation, dumping of garbage, and depleted sources of water, which calls for the immediate attention of the government to revive these to their original shape and conditions. Similar issues can be identified across the country as most of the cities identified under the Smart City initiative are already experiencing water scarcity. Hence, it is essential to map the coordinates of all water bodies in a single platform to monitor, control, and prevent pollution and in parallel make the people aware of the importance of protecting these water bodies locally from becoming extinct. Healthy water bodies, such as wetlands, help the ecosystem stay rich in biodiversity. Since sewage treatment plants (STPs) are set up for treatment of wastewater flowing into the water bodies, the quality parameters of the wastewater and accordingly the process design of the STP must be done properly to ensure collection of tertiary treated effluent in water bodies. The regulating authority must check the quality of water in water bodies periodically.
CONCLUSION
Temporal analysis of water bodies using high-resolution satellite imagery for pre- and post-monsoon surveys can be done to understand the availability of a source of water, its quantity, and quality in tanks, ponds, lakes due to rainfall, or due to some other sources such as flooding water from canals and water from rainwater harvesting channels. In parallel with that, the water quality analysis can be done using a comprehensive field visit. The second step can be to identify the probable source of pollution. This information can be used for prioritising the water bodies for rejuvenation. Public participation by mass awareness campaigns can lead towards behavioural changes in society, and this can be the core of the conservation plan.
It is necessary to use recycled water of bathing standard along with the rainwater to inject into the ground to recoup the drawdown of water table in Delhi. The rejuvenation of water bodies and creation of artificial water bodies are the probable solutions to increase groundwater sources in future. In addition, community level/large-scale rainwater harvesting through stormwater drains, large parks, check dams, ridges, and forests should also be adopted for groundwater recharge at large scale to maintain the balance between extraction of groundwater and its replenishment at the same time. To improve the efficiency of replenishment rate, impervious layers of soil should be replaced with sand or filter media. To avoid the possible contamination of the groundwater in the process of replenishment with recycled water, it is essential to monitor the water quality of the recycled water from STPs as well as in the water bodies regularly so that the quality of water being percolated into the ground is assured. A monitoring bore well should also be installed for regular monitoring of groundwater quality. The enforcement of environmental laws to protect the water bodies must be done diligently by the concerned regulating authorities.
There are two ways to supplement the gap between demand and supply. One is either to use recycled water directly for non-potable purposes or to manage groundwater recharge with rain and recycled water to enhance sustainability of the groundwater source. The Delhi Government should make its best offices use the recycled water for potable and non-potable uses. Thus, if rainwater and recycled water are used for groundwater recharge through static water bodies, the problem of drinking water may be resolved in Delhi to a large extent, as groundwater from the periphery of these rejuvenated water bodies can be further extracted for drinking after proper treatment.
With encouraging results achieved in these two water bodies of Delhi, wherein the water table has risen up to 5–7 m in addition to the improvement in the quality of the groundwater, the water bodies elsewhere in India and abroad can be rejuvenated and the groundwater can be replenished with recycled water in a similar sustainable manner creating additional water resources.
ACKNOWLEDGEMENT
We are thankful to Delhi Jal Board officers for providing the information about the Pappankalan artificial lake and the groundwater quality parameters after the construction of the lake.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.