Sufficient water is available to meet everyone’s requirement, provided (i) water harvesting is undertaken through surface water bodies; this requires rejuvenation of lakes and reestablishment of interconnectivity; harvesting of rainwater (at decentralized levels), treatment;   (ii) treatment and reuse of sewage. However, the success of sustainable water path depends on the political will, bureaucracy shedding their colonial style of functioning and more importantly citizen’s assertion for their right for equal quantity and quality of water.

Average annual rainfall in Bangalore is about 787 mm with 75% dependability and return period of 5 years. Catchment wise water yield analysis indicates about 49.5% (7.32 TMC) of water yield in the Vrishabhavathi valley (including Arkavathi and Suvarnamukhi), followed by 35.2% (5.2 TMC) in Koramangala Challaghatta valley and 15.3% (4.2 TMC) in Hebbal valley and the total annual water yield in Bengaluru is about 14.80 TMC. Domestic demand of water (at 150 lpcd) is 20.05 TMC per year (1573 MLD). This means about 73% of Bangalore’s water demand can be met by efficient harvesting of rain water. Quantification of sewage generated shows that about 16.04 TMC (1258 MLD) of sewage is generated in the city.

Sewage treatment with complete removal of nutrients and chemical contaminants can be achieved by adopting decentralized treatment plants similar to the success model (secondary treatment plant integrated with constructed wetlands and algae pond) at Jakkur lake. In addition to this, water available with efficient rainwater harvesting is about 14.8 TMC. This accounts to total of 30.85 TMC of water that is available annually would cater the demand of 20.05 TMC, provided the city administration opts for decentralized optimal water management through (i) rainwater harvesting by rejuvenating lakes - the best option to harvest rain water is through interconnected lake systems, (ii) treatment of sewage generated in households in each locality (opting the model functional since 2010 at Jakkur lake – STP (Sewage Treatment Plant) integrated with constructed wetlands and algal pond; (iii) conservation of water by avoiding the pilferages (due to faulty distribution system); (iv) ensuring water supply 24x7 and (v) ensuring all sections of the society get equal quantity and quality of water.  Rejuvenating lakes in the region helps in retaining the rain water. Treating sewage and options to recycle and reuse would minimize the demand for water from outside the region.

However, this model of decentralised harvesting of water and reuse of treated sewage is not an attractive proposition for the current breed of decision makers with the colonial style of functioning/mind-set. The financial gain is much higher in the case of mega projects (such as water diversion) compared to these decentralised models. This is the sole reason for the local administrators to degrade decentralised water harvesting structures and alienating local community. The main reason for deliberate inefficient management of water resources is to maximise the net return for the ruling class themselves than the overall growth of the region with water security.  The analysis illustrates that the city has at least 30 TMC (Bangalore city) of water, which is higher than the existing demand (20.08 TMC, at 150 lpcd and 2016 population), if the city adopts 5R’s (Rejuvenate, Retain,  Recycle - Reuse, and Responsible citizens’ active participation with good governance).

Scope for decentralized rainwater harvesting: During 1800, the storage capacity of Bangalore was 35 TMC. In 70’s, lakes covered an area of nearly 3180 hectares  and now the spatial extent of lakes cover an area of 2792 hectares. The current capacity of lakes is about 5 TMC and due to siltation, the current storage capacity of the lakes is just about 1.2 TMC, i.e., nearly 387 hectares of water bodies disappeared besides reduction in the storage capacity by 60%. Bangalore being located on the ridge, forms three watersheds – Koramangala Challagatta valley, Vrishbhavathi Valley and Hebbal Nagavara Valley.  Earlier rulers of the region, created interconnected lake systems taking advantage of undulating terrain.  Number of lakes in the Koramangala Challaghatta Valley is about 81, followed by the Vrishabhavathi Valley (56) and the Hebbal Nagavara Valley (46). In order to enhance the water retaining capability in the catchment, it is essential to rejuvenate lakes and undertake large scale watershed programme (soil and water conservation). Lakes are the optimal means of rainwater harvesting at community level. This entails

Land use analysis in Bangalore City shows 1028% increase in urban (built-up) area between 1973 and 2017 i.e., from 8.0%  (in 1973) to 78% (in 2017). Land use prediction using Agent Based Model showed that built up area would increase to 93.3% by 2020, and the landscape is almost at the verge of saturation.
Background: Water is one of the fundamental elements of the universe from which early life originated millions of years ago on earth. Every life on the earth is primarily dependent on water which hosts innumerable aquatic species from single cell creatures to gigantic blue whales. As the evolution of human took place, civilized human settled down on the fertile river banks. In other words, river banks are the motherhood for civilized human and most of the civilization around the world. These river or lake banks gave water for drinking and also for cropping along with mineral rich soil. Civilized men knew the importance of water and respected these water bodies. Advantages of traditional water harvesting structures are:

However, these practices took backseat, during the imperial period (1800 till independence i.e. 1947) of British rule with the push for large scale river valley and canal projects and also due to lack of maintenance and management of small water harvesting structures. Apart from this, high and oppressive taxes and irrigation cess (towards the repair works of these structures) led to the decimation of irrigation tanks during the period of colonial rulers.

The centralized irrigation systems coupled with increased incidences of untimely rainfall and higher temperature, lack of annual maintenance, deforestation in the catchment and receding community participation, led to the decline of thousands of traditional water harvesting systems. As a consequence of these, the thousands of lakes and tanks are silted with the decrease in the overall storage capacities and groundwater recharge. Unplanned urbanization has led to the increase in urban conglomerates, with drastic reduction in land cover of the catchment, which substantially reduced the water holding capacity of the catchment. Higher incidences of flooding and soil erosion, is the direct consequence of damaging the water harvesting structures. Therefore, it is necessary to inculcate the traditional knowledge on sustainable water harvesting and management practices in the educational curricula. At a village/ward level it’s necessary to identify the appropriate investment strategies and make the local Panchayats/ward member responsible for the operation and maintenance of the tanks. This will help in adopting the decentralized water harvest and management practices in the arid and semi-arid regions that are economical and technically feasible alternative to meet the regional water demand.

A well-known and success model of lake ecosystem is at Jakkur in Bangalore with integrated wetlands ecosystem (Secondary treatment plant integrated with constructed wetlands and algae pond). Complete removal of nutrients and chemical contaminants happens when treated sewage (secondary treated) passes through constructed wetlands and algae pond, undergoes of bio-physical and chemical processes. The water in the lake is almost potable with minimal nutrients and microbial counts. This model has been functional successfully for the last 5 years after interventions to rejuvenate the lake. This system is one of the self-sustainable ways of lake management while benefitting all stakeholders - washing, fishing, irrigation and local people. Wells in the buffer zone of 500 m now have higher water levels and without any nutrients (nitrate). Groundwater quality assessment in the same region, before rejuvenation of Jakkur Lake had higher nitrate values.  Adoption of this model also ensures nutrient free and clean groundwater, which helps in achieving the goals of providing clean water to the local community.

Another very good example of constructed water body is of the centenary pond at IISc, created solely to harvest rainwater. Taking advantage of undulating terrain in the campus, storm water drain is routed to a low lying area. The spatial extent of the water body is about one hectare and stores on an average 0.1 million liters. This water body is now an abode of a variety of aquatic animals and has been an attractive to several resident and migratory birds. The creation of these water bodies has helped in a good ambience and maintaining a good biodiversity in the region besides providing a very good aesthetics and is a now a means of stress relief for the students learners of higher education. These successful experiments highlight that water quality can be maintained to meet the local requirements by optimal management of bio-physical dynamics in a water body.

Deterioration of traditional water harvesting practices in other parts of burgeoning Bangalore has resulted in the inequity in water distribution and growing water scarcity, which has escalated water conflicts during the 20th century. Irresponsible management of natural resources is evident from

Due to these unauthorized practices, vital constituents of the landscape (wetlands and drains,) have become breeding ground of disease vectors, stinking cesspool and emitters of GHG’s (Greenhouse gases: methane, carbon di-oxide, etc.), etc. These practices are posing serious threat to public health and hygiene with an irrecoverable loss in aquatic biodiversity. Unplanned and un-coordinated rapid urbanization has further stressed the natural resources in the region. The water demand of the urban conglomerates is met with piped water supply or from water transported from distant areas. Coupled with this, substantial degeneration of the traditional knowledge has resulted in deterioration of tank management practices. Sustainable water management of water resources through revival of traditional water harvesting strategies and comprehensive watershed restoration and management by involving local stakeholders is essential for adequate groundwater recharge and for maintaining water balance in the region.

Recommendations: The restoration and conservation strategies has to be implemented for maintaining the ecological health of aquatic ecosystems, aquatic biodiversity in the region, inter-connectivity among lakes, preserve its physical integrity (shorelines, banks and bottom configurations) and water quality to support healthy riparian, aquatic and wetland ecosystems. The regular monitoring of water bodies and public awareness will help in developing appropriate conservation and management strategies.

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