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Bengaluru, the capital city of Karnataka, India, stands as a vibrant metropolis known for its technological prowess as well as rapid urbanization. With a population estimated to be over 14 million in 2024 [1], the city has experienced exponential growth, leading to unprecedented demands on its infrastructure, particularly its water resources.

The city's water needs are primarily met through surface water source supplemented by borewell waters, managed by the Bengaluru Water Supply and Sewerage Board (BWSSB). However, the rapid expansion of the city has strained existing water resources, leading to over-exploitation of groundwater and reliance on private water tankers [2].

While the inner zone of Bengaluru benefits from piped water supply sourced from the Cauvery River, the outer zones grapple with a mix of surface water and groundwater sources, exacerbated by a burgeoning population and booming real estate development.

Media reports during February-March 2024 have widely highlighted the issue of Bengaluru running dry especially in the peripheral parts of the city.

The rampant rise in prices of private water supply tankers and subsequent government interventions by the Bruhat Bengaluru Mahanagar Palike (BBMP), underscore the fragility of Bengaluru's water ecosystem.

Hydrogeologically, Bengaluru city is predominantly covered by hard rock aquifers comprising of granites and gneisses with pockets of schistose rocks and migmatites of Archean age. Central Ground Water Board (CGWB) has been carrying out ground water exploration activities to study about the hydrogeology, aquifer parameters and groundwater potential in the city as well as the district since its inception. Based on the studies it has been found that yield of the borewells generally varies between <1 litres per second(lps) to 2.5 lps with isolated cases of yield upto 4.3lps. The transmissivity value generally ranges between 2m2 /day to 40m2 /day with isolated cases reaching upto 281 m2 /day [3]. Thus the sustainability of hard rock aquifers is low owing to inherent limited storage potential and limited yielding capacities.

This paper seeks to shed light on the underlying causes of Bengaluru's water woes and propose strategies for effective water management.

Study area

The study area occupies an area of 711 sq.km. The study area is formed by parts of 5 taluks of Bengaluru urban district namelyBangalore North, Yelahanka, Bangalore East, Bangalore South and Anekal taluk (Figure 1).

 

Figure 1: Index map.

There are three watersheds in the study area namely: upper Ponnaiyar watershed to the East, lower Arkavathy watershed to the South and South-West and Kumudavathy watershed to the North-West (Figure 2). The local topography is characterized by a series of welldefined valleys which radiate from a ridge of high ground to the north of the city and fall in a cascading manner towards wide belt of flat land extending beyond the limits of the metropolitan area to the South.

 

Figure 2: Digital elevation model of Bengaluru city and surroundings.

The water supply data for the city was obtained from the Bangalore Water Supply and Sewerage Board (BWSSB). Domestic water demand was calculated based on the UN population projections. The annual rainfall data from 2013 to 2023 was obtained from the Karnataka State Natural Disaster Monitoring Centre (KSNDMC). The decadal average annual rainfall was calculated for comparison with annual rainfall of 2023 [4]. The Ground Water Resource Assessment (GWRA) results of 2022 and 2023 for city were taken from Dynamic Groundwater Resource, Karnataka report of CGWB. Land Use-Land Cover (LULC) layers of the year 2000 and 2010 in 1:50000 scale was obtained from Karnataka State Remote Sensing Application Centre (KSRSAC). Land Use-Land Cover (LULC) layers of the year 2020 in 1:10000 scale was obtained from Regional Remote Sensing Centre, ISRO, Bengaluru. The various thematic layers were prepared using ArcMap 10.5 software [5].

The results and discussions are based on various studies being undertaken by CGWB in Bengaluru city and the continues and ongoing activities like water level monitoring. Based on this, the water demand vis-a-vis supply scenario, rainfall comparison, ground water resource assessment, change in land use-land cover pattern, water level scenario both present and long term has been studied and various causes of the scarcity are delineated below:

Water demand vis-a-vis supply

Bangalore's 2024 population is now estimated at 14,008,262. Bangalore has grown by 4,00,462 in the year 2022, which represents a 2.94% annual change. These population estimates and projections come from the latest revision of the UN World Urbanization Prospects. Considering 135 litre per capita per day (lpcd) of water requirements as per National Building Code (NBC) 2016 norms, the domestic water requirement of Bangalore City can be estimated as 1891 Million Litres per Day (MLD) [6]. The current water supply to city is about 1273 MLD after accounting for the conveyance losses and drying up of borewells. Thus, the current deficit in March-April, 2024, works out to be about 618 MLD (Table 1).

Table 1: Water demand, supply and deficit comparison for the city (values in MLD).

Comparison of rainfall of Bengaluru city

During the year 2023, the actual annual rainfall received in Bengaluru city was 686 mm against the decadal average annual rainfall of 1101.58 mm. There was 37.75% deficit in rainfall in 2023 as compared the decadal average annual rainfall. If we compare it with the actual annual rainfall received in 2022, then the deficit is still more. The actual annual rainfall received in the year 2022 was 1368.93 mm, whereas the actual annual rainfall received during the year 2023 was 686 mm which is 50% less as compared to 2022 (Table 2).

Table 2: Comparison of rainfall of Bengaluru city.

Comparison of ground water resources of Bengaluru city

The Ground Water Resource Assessment (GWRA) results of 2022 and 2023 were compared to understand the change in ground water condition in Bangalore city [7]. Compared to year 2022 there is decrease of ground water recharge through rainfall from 1991.95 ham to 1853.53 ham in 2023. The decrease in annual extractable ground water is also observed in comparison of 2022 and 2023 results from 2377.9 ham to 2128.2 ham. Further, increase in ground water extraction is observed from 4580.3 ham to 4626.7 ham which has resulted in increase in stage of ground water extraction from 192.62% to 217%. Thus, the annual recharge, availability and stage of extraction has deteriorated in Bangalore city in the year 2023 as compared to the year 2022 (Figure 3). The city is categorized as Over exploited with respect to ground water resources [8].

 

Figure 3: Graph showing comparison of dynamic ground water resources of Bengaluru city in 2022 and 2023.

Comparison of Land Use–Land Cover (LU-LC of Bengaluru city

The city area in year 2000 was approx. 522 sq.km which subsequently increased to 674 sq.km in 2010 and to 711 sq.km in 2020. However, for comparison of different areas, the land use pattern has been taken for the current city area comprising 711 sq.km. The perusal of the Table 3 shows that the built-up area has increased from 42% in the year 2000 to 55% in year 2010 and 86% in the year 2020, whereas the vegetation area has decreased from 45% to 8% and water bodies areas has also decreased from 8% in 2000 to 4% in 2020 (Figures 4 and 5). There has been significant encroachment and extinction of waterbodies in the city. As evident from Table 4, the overall total runoff generation has increased by 20.25% in 2010 and by 66.46% in 2020 as compared to the year 2000. For built up area, the runoff has increased manifold by 31.54% in 2010 and 105.37% in 2020 respectively as compared to the year 2000, whereas the runoff from vegetation and open areas has decreased considerably by 82.45% and 67.57% respectively in 2020 [9].

The changing land use pattern is increasing surface runoff and reducing potential to recharge ground water and causing drying up of borewells during deficient rainfall periods.

Table 3: Comparison of change in LULC pattern in Bengaluru city from 2000 to 2020.

Table 4: Runoff calculations based on LULC areas of Bengaluru city.

 

Figure 4: Change in LU-LC of Bengaluru city in two decades.

 

Figure 5: Change in the area under waterbodies in Bengaluru city over the two decades.

Comparison of ground water level scenario of Bengaluru city

In any major urban areas, the use of ground water is governed by presence or absence of surface water supply network and Bengaluru is no exception to that. Thus, it was necessary to know the Cauvery water supplied areas and non-Cauvery water supplied areas of the city. The ward wise areas completely covered by Cauvery water and partially covered with Cauvery water were plotted to get the spatial distribution of these areas (Figure 6). From the map it is observed that the areas in the peripheral parts lack good provision of Cauvery water.

 

Figure 6: Areas fully and partially covered by Cauvery water supply of BWSSB.

The seasonal comparison of water level was done by comparing pre-monsoon and post monsoon water levels for the year 2023. During pre-monsoon 2023 (Figure 7), the water level in piezometers/ borewells located in the peripheral areas, which are not covered by Cauvery water supply network is more than 30 metre below ground level (mbgl), whereas areas with Cauvery water supply are having water levels in the range of 5 to 30 m bgl. Normally in post-monsoon season, the water level comes up if the recharge due to rainfall is sufficient, however a reverse phenomenon is observed in the year 2023 especially in peripheral areas without Cauvery water supply network as evident from the map (Figure 8) and the Table 5. Thus, it is evident that the water levels are shallow in central/core part of the city which are completely covered by Cauvery water supply and water levels are deeper in the peripheral areas which are partially covered by Cauvery water supply. This is creating more stress on ground water resources in peripheral areas and leading to drying up of bore wells.

Table 5: Comparison of area under various depth to water levels in pre and post-monsoon period 2023.

 

Figure 7: Pre-monsoon 2023 depth to water level map of deeper aquifer.

 

Figure 8: Post-monsoon 2023 depth to water level map of deeper aquifer.

Generally during post-monsoon period rise will be observed in ground water level when there is good rainfall and recharge, but in 2023 rainfall has been deficit to the tune of 50% as compared to the year 2022 resulting in deepening of post-monsoon water levels. The areas under deeper water levels have increased mainly in peripheral areas by 29% in 30 to 40 mbgl range, by 36% in 40 to 50 m bgl range and by 41% in >50 m bgl range.

The annual as well as long term i.e., decadal comparison of water level was also done by comparing the water levels of January 2024 with January 2023 (Figure 9). The long-term comparison was also carried out by comparing the decadal mean of January 2014-2023 with January 2024 water levels (Figure 10). The annual as well as decadal comparison indicates that all the wells have recorded fall in water levels. The area under more than 4 m fall is more in decadal fluctuation map as compared to annual fluctuation map indicating that the fall in water levels is more pronounced during the decadal comparison.

 

Figure 9: Annual water level fluctuation map.

 

Figure 10: Decadal mean water level fluctuation map.

• The water scarcity situation developed in Bengaluru city is manifestation of multiple factors like increased population, unplanned development leading to increased concretization, rapid urbanization, strained infrastructure and dwindling ground water resources. Both supply side as well as demand side interventions coupled with strict implementation of existing regulatory measures is required to tide over the situation. The recommendation focusses on both short and long-term measures.
• The several large defense establishments where ground water withdrawal is minimum. Such places may be targeted for construction of additional water supply wells after site specific integrated hydrogeological investigations. The wells are to be used only during drought conditions/water scarcity.
• As per the LU-LC data, 3200 ha of area is occupied by water bodies, which are primarily lakes and ponds. These water bodies should be immediately taken up for de-silting. Considering the minimum depth of 1 m of desilting, the additional storage potential that can be created is 3200 ham. Such an initiative will help in recharging the underlying ground water aquifers and increase the sustainability of the aquifers during lean/summer period.
• BWSSB has 36 Sewage Treatment Plants (STPs) whose capacity is 1527.5 MLD. It is treating 1091.54 MLD sewage. Out of 1091.54 MLD, 923 MLD treated sewage is reused and 168.37 MLD goes to Storm Water Drains (SWDs). This 168.37 MLD treated water from STPs may be utilized for the needs of public. The treated water from STP’s which is available throughout the year conforming to CPCB standards may be used for recharging lakes/ponds within the city. To ensure the quality of the treated water, an online system of water quality monitoring before release into the lakes and ponds should be installed.
• Treated wastewater from commercial establishments can be provided to water scarce areas for non-potable domestic use.
• The rain water runoff generated along the major roads and metro lines/stations needs to be harvested and used for either storage or recharge of deeper aquifer after proper filtration.
• The parks, grounds, open spaces need to be utilized for rain water harvesting by construction of recharge trenches, recharge pits and other suitable recharge structures.
• Water saving fixtures like flow aerators should be fitted in houses/ residential complexes/companies/bulk consumers etc. Individual households should be encouraged to reduce the demand by using bucket for bath instead of shower, re-use RO reject water for nonpotable use. Such small measures, if adopted by all will go a long way in reducing the water demand.
• BWSSB imposed ban on using fresh water for building construction, cleaning of vehicles is hardly adhered to. BBMP Marshalls should patrol the neighborhoods to curb such actions and impose strict fines.
• Karnataka Ground Water Authority (KGWA) should bring bulk water suppliers (tanker water suppliers) under its regulation as per Central Ground Water Authority (CGWA) guidelines, so as to regulate the rampant use of ground water.
• The regulation to stop encroachment of lakes, water bodies and penal provisions are already existing by means of Karnataka Tank Conservation and Development Authority Act, 2014. It needs to be implemented rigorously on ground to achieve its objective.
• Rain water harvesting has good scope in replenishing the water Table 4. Proper implementation of the rain water harvesting act 2009 amended in 2021 of BWSSB for harvesting and recharge of rain water. As per the Bangalore water supply and sewerage (Amendment) Act, 2021, Section 72A, it is obligatory to provide rainwater harvesting structure for all construction on site areas of 30 feet × 40 feet admeasuring 1200 sq. feet and above. This will also contribute to reduce the stress on the water carrying capacities of storm water drains.
• Rain water harvesting cell should be created in each ward by BWSSB/BBMP to impart training to volunteers and technical knowledge dissemination by CGWB/GWD for better implementation of the RWH/AR structures.
• In large apartment complex/high rise/multistoried buildings, individual flat/household should be provided with water meter, so that the individual owner can be charged accordingly instead of the uniform rates for all users. This will automatically reduce the water consumption as individual will be charged.
• Identifying and developing alternate source of surface water supply to Bangalore city like Yettinahole or Mekadetu projects as a longterm measure to keep pace with the increasing water demand of the city.
• Overall, a comprehensive approach involving regulatory interventions, community engagement, and sustainable water management practices is crucial to mitigate the water crisis in Bengaluru and ensure the city's long-term water security.

The authors are grateful to Dr. Sunil Kumar Ambast, Chairman, Central Ground Water Board for permitting the submission of this paper. The authors are also grateful to Shri N. Jyothi Kumar, Regional Director, CGWB, Bengaluru for his guidance and encouragement in publishing this work.

Rahul R. Shende, Suchetana Biswas, Caroline Louis: Conception and design of the study, project planning and execution, methodology adoption.

Suchetana Biswas, Caroline Louis, N.C. Sahoo: Fieldwork and data acquisition.

Suchetana Biswas, Rahul R. Shende, Caroline Louis, Lubna Kouser: Analysis and interpretation of data, preparation of GIS maps.

Suchetana Biswas and Rahul R. Shende: Drafting and revising the manuscript critically for important intellectual content.

The authors declare that there is no conflict of interest.

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