Keeping pace with the rising water demand is a critical challenge faced by urban water supply departments globally. Bengaluru, once known as the ‘City of Lakes’ is a prime example of an urban agglomeration with diminishing water resources despite its rich legacy of innovative water management.
A recent study conducted by school students as part of the Anveshana research project sheds light on the transformative potential of rejuvenating Bengaluru’s lakes to achieve water self-reliance.
This article delves into the historical significance, current challenges and future possibilities of Bengaluru’s lakes, revealing how these water bodies could hold the solution to the city’s water crisis.
Historical practice of water management included human-made lakes along the stormwater network to store the rainwater for domestic and agricultural purposes.
These lakes were meticulously designed, not just as storage units but as a chain of interconnected reservoirs. Rainwater would flow from one lake to another, ensuring maximum storage and efficient use.
This system supported agriculture, drinking water needs and groundwater recharge, making the region largely self-sufficient. In the Bengaluru region, these lakes were central to the city’s growth and prosperity.
The interconnected system also acted as a flood management tool, absorbing excess rainfall during the monsoon and releasing it gradually. The design reflected a deep understanding of local geography and rainfall patterns, offering a sustainable solution to water management.
Over the years, urbanisation and changing priorities led to the decline of Bengaluru’s lake system. The shift from reliance on surface water to borewells for groundwater extraction was one of the primary reasons for neglecting lakes. As the city’s population increased, lakes were encroached upon for residential and commercial developments, turning many of them into sewage dumps or dry wastelands. This neglect led to the degradation of lake ecosystems, sedimentation, and the loss of many smaller water bodies.
With gradual increase in water demand and advent of groundwater extraction and canal system, the city began to import water, earlier from Hesaraghatta and Tippagondanahalli on Arkavathi River and then post 1964, from Krishnaraj Sagar reservoir on Cauvery River. This led to gradual loss of the lake and tank water system.
Additionally, in the last few decades, Bengaluru has witnessed growth in the field of industrial, commercial and institutional sectors.
This urbanisation led to population growth from 4.08 million in 1991 to 5.8 million in 2001, which increased to 8.5 million in 2011 with a projected estimated growth as shown along with increasing water demand in the illustration (BWSSB archives).
An independent assessment, of water demand supply gap in Bengaluru city, estimated that for a projected population of 9.7 million people by the end of year 2025, domestic water demand will be about 2314 million litres per day (MLD) which is about 514 MLD higher than the available water (1800 MLD).
This demand-supply gap will further increase by next decade with a projected population of 12.6 million people (JICA report, 2017); it will increase by several orders of magnitude when industrial and agricultural demands are also taken into account.
Furthermore, an estimate of water supply to Bengaluru shows that currently the city’s demand for freshwater stands at approximately 2,632 million litres per day (MLD). Towards this, about 50 per cent of the demand (1460 MLD) is supplied through Cauvery river water whereas the remaining 50 per cent (1372) is procured from groundwater borewells (Well Labs, Bengaluru).
Proper utilisation of rainwater through efficient rainwater harvesting, lake rejuvenation, and catchment area management could help meet the city’s growing water demands sustainably. The entire Bengaluru district region, including the 2,259 km² of rural land and 2,174 km² of urban land, receives an average 952 mm of rainfall every year.
This rainfall amounts to approximately 4,220 billion litres of water annually. Out of this, 45 per cent goes to evapotranspiration, leaving 2,321 billion liters as surface runoff, which is 55 per cent of the total rainfall. This volume of surface runoff presents a significant opportunity for addressing Bengaluru’s water needs.
To achieve this, strategic initiatives are needed, including restoring lakes as reservoirs for runoff storage, mandating rooftop rainwater harvesting in urban areas, and improving soil infiltration in catchment areas to reduce siltation.
However, due to the degraded state of lakes and improper water management, a significant portion of this rainwater goes to waste as runoff. By restoring these lakes to their former capacities, the city can tap into a sustainable water source that reduces dependence on external supplies.
A student-led research initiative at Prayoga provides valuable insights into the current state of Bengaluru’s lakes.
Their findings are both alarming and enlightening — The number of lakes in the region decreased by 14 per cent, from 3,835 in 2011 to 3,379 in 2024. Despite this, there hasn’t been a significant reduction in lake area, suggesting the decline is primarily in smaller lakes.
An analysis of lake conditions based on lake area reveals an unexpected trend: more lakes are in a wet state in 2024 compared to 2011.
At first glance, this might seem like a positive development, but a closer examination uncovers a troubling reality.
The increased ‘wetness’ of these lakes is primarily due to a rise in urban wastewater being discharged into them, turning these vital water bodies into sewage reservoirs.
This influx of untreated waste has severely degraded their ecosystems, undermining their natural function as water storage and recharge systems.
These findings underscore the urgent need for comprehensive lake rejuvenation efforts to halt further ecological damage and restore the lakes’ capacity to serve as valuable water resources.
Reviving these ecosystems is crucial not only for preserving biodiversity but also for tapping into their potential to contribute to the region's water sustainability.
The student project suggests actionable solutions to revitalise Bengaluru's lakes: Planned Excavation to remove a few meter thick layer of sediment from lakes can significantly increase their storage capacity.
This excavation would not only deepen the lakes but also restore their ability to recharge groundwater effectively. (2) Ensuring that rainwater flows freely into lakes by cleaning and maintaining catchment areas is crucial. This would reduce contamination and improve water quality. (3) Encouraging local communities to participate in lake management can foster a sense of ownership and ensure long-term sustainability.
The cost of water supply to Bengaluru from the Cauvery River is a significant operational expense, encompassing pumping, treatment, and distribution. With a supply of 1,350 MLD (million liters per day) and an average cost of Rs 28 per kilolitre (1,000 litres), the daily expense for providing water from the Cauvery River amounts to approximately 37.8 million per day (BWSSB). However, this figure can vary depending on factors like electricity rates, infrastructure maintenance, and operational efficiencies.
Rejuvenating lakes offers significant economic benefits compared to the high cost of sourcing water from the Cauvery River.
The costs associated with excavation and maintenance are far outweighed by the savings in water procurement and treatment expenses. Moreover, the sediment removed from lakes during excavation has potential industrial and agricultural applications. If utilized effectively, this byproduct can offset rejuvenation costs, making the initiative economically viable. Such programs not only address water scarcity but also create jobs and promote local economies.
Hence, Bengaluru’s lakes, once integral to the region's water management, offer a path to solving the city’s growing water crisis. With proposals from young researchers for lake rejuvenation — including excavation to restore storage capacity and catchment cleaning to maximize rainwater retention — the city can reclaim the efficiency of historical practices while addressing modern water needs.
The student project highlights the economic feasibility of this approach, as excavated sediments can be reused industrially and agriculturally, offsetting costs. Revitalising these lakes not only promises water self-reliance but also sets a sustainable example for urban centers nationwide. By restoring these vital water bodies, Bengaluru can not only address its immediate water demands but also create a sustainable model for other urban areas to emulate.
It is time for collective action to revive these invaluable resources and secure a water-sustainable future for the city.
Ajit Singh is Principal Researcher in the Department of Earth Sciences, Prayoga Institute of Education Research
Views are authors' own and do not necessarily reflect those of Down To Earth