This article published in the journal Current Science has been written in response to the earlier article published in Current Science that highlights the acute water scarcity that the city of Bangalore has been facing over the years and examines the current availability of resources and recommends protection and conservation of stormwater discharge and use of treated sewage water to meet the water needs of the population, rather than the uneconomical and anti environmental proposals like diversion of water from the rivers such as the Nethravati or the Krishna.

The authors of this article disagree with the points and proposals raised in the earlier article regarding the solving of the water crisis in Bangalore by arguing that given the limitations of the proposals recommended by the authors, the river diversion schemes could be inevitable for the reasons mentioned in this note. In addition, it is pertinent to look at the water problem from a river basin perspective where better options with long-term perspectives can be searched to manage the water crisis of Bangalore city.

The authors argue that:

• In the earlier article, water balance for Bangalore city from the perspective of quantity has been looked upon, but the  issue of quality has been ignored, which can upset any water balance. Rather, the groundwater within the unconfined aquifer around Bangalore has been identified as groundwater quality hotspot based on certain water quality parameters such as iron, fluoride, nitrate and conductivity which are found to be exceeding their permissible limits and studies have confirmed the deteriorating groundwater quality and increasing health hazards around Bangalore city, which can lead to considerable social costs to deal with health of populations in the future.
• The  figure of groundwater overdraft of 12,741 ha-m/yr, as an assured source of water for Bangalore is unreliable. Hence the demand–supply gap remains at 23,677 ha-m/yr and that can trigger a massive water-cum-health crisis amongst as many as 47 lakh people, i.e. about 50% of Bangalore city population by 2020 (considering a projection of 95 lakh population). To avert the possible water crisis, it is relevant to keep open the option of inter-basin transfer of water from west-flowing rivers like Nethravathi or water transfer from long distance like River Krishna instead of viewing the diversions purely from cost economics and environment point of view.
• The viewpoint in the earlier article that 17,040 ha-m/yr of surface run-off as being wasted is incorrect. If this water is used for Bangalore city, then the loss to the Cauvery basin water budget can only be augmented from the other diversion like Nethravathi–Hemavathy link. The authors argue that the suggestion that waste water recycled at the tertiary level could be brought to safe standards of drinking water and domestic usage is like assuming the process as simplistic, which is quite misleading. To bring the recycled water to the standards of domestic use, the treatment process is much beyond the tertiary level that includes microfiltration, reverse osmosis and UV/ozone treatment followed by recharging groundwater aquifers or releasing into reservoirs for natural purification,where the water again is sent for normal treatment process before delivering for domestic use.
• Getting recycled water treated for domestic consumption should match the technology and professionalism seen in countries like Singapore. The authors  have not provided any cost economics to show that waste water recycling is a viable option for Bangalore than river diversion. So, the impression created by  authors that the recycling and reuse of waste water alone would completely redress the future water crisis is incorrect, except that it may be a partial water solution, that too only after overcoming the constraints.
• The contaminants of Bangalore waste water are diverse ranging from normal domestic sewage load to industrial waste comprising heavy metals, pharmaceuticals, pesticides called ‘emerging contaminants’ and there is no one single method that can remove the entire range of contaminants and ensure that the water is fit for domestic consumption. While the standard treatment processes like membrane technology, UV/ozone treatment can remove the organic and inorganic load, it requires better technology to remove pharmaceutical contaminants like antibiotics, hormone supplements, etc.

The article recommends that since irrigation is the largest consumer of water and hence, from the perspective of the water-scarce river basin, if the water-intensive crops in the basin are replaced with less water intensive crops, along with incentives for conserving water, applying higher or discriminatory water rates, then substantial amount of water can be spared to cater to the growing thirst of Bangalore city

The article ends by arguing that for a comprehensive long term water solution for Bangalore city to cater to a projected population of about 95 lakhs and more by 2020, a combination of measures like spreading out the development to other smaller towns/ cities of the basin like Mandya and  Hassan or even in Tamil Nadu, reduction in cultivation of water-intensive crops in the basin, increasing the water productivity of crops, long-distance water transfer and river diversion should be considered. These basin scale water management measures are in addition to the option of recycling of waste water,but only where it can overcome the constraints of technology, space, topography of Bangalore city, cost economics and then where it does not affect other regions of Cauvery basin and basin comprising east flowing river systems.

The article can be accessed at this link