The recent water crisis in Tamil Nadu requires attention in the Budget. First let us consider how to increase the supply of water. The annual rainfall in India is 4000 Billion Cubic Meters (BCM). After accounting for evaporation, the availability is 1869 BCM. Some of this water flows in remote areas and cannot be harnessed leaving 1123 BCM of utilizable rainfall. Of this,690 BCM is surface water that flows in streams and rivers and 433 BCM is the water that percolates into the groundwater aquifers.
There is possibility of increasing the amount of water available at each of the above steps. Less water will evaporate if we can quickly reach it below the soil. The rain water can be taken to recharge wells. Secondly, the surface water in remote areas which is considered not usable, can be harnessed. It is only a matter of cost. For example, harnessing rainfall from Cheerapunji and reaching it to Bengal is only a matter of cost. My guesstimate is that we can get an additional 200 BCM water from these measures.
The third step is to reconsider the policy of storing water in reservoirs. Of the 690 BCM harnessed surface water mentioned above, 253 BCM was stored in large reservoirs like Sardar Sarovar, Bhakra and Tehriin 2010. This storage leads to loss of water in many ways. One, about 15 percent of the water is lost to evaporation from these reservoirs. Two, the organic matter ferments in the bed of these reservoirs and produces methane that is adding hugely to global warming which, in turn, is disturbing our rainfall pattern. Rainfall is occurring in short spells which makes it difficult to use it for recharge of ground water. I guesstimate the loss from this to be 5 percent of the storage capacity. Three, water is wasted in the process of transportation to the fields through canals. I reckon this loss to be 15 percent. Four, holding the flows in the reservoirs reduces the spread of water in the rivers downstream leading to less groundwater recharge and less irrigation downstream. I reckon this loss to be 10 percent. The total water lost, therefore, from reservoirs is about 40 percent of their storage capacity or 101 BCM.
All these problems can be solved if we store the rainwater in groundwater aquifers instead of reservoirs. One, water does not evaporate from aquifers. Two, organic matter does not reach the aquifers and does not ferment. Methane is not produced.
Three, water is extracted from the ground where required hence there is no loss during transportation. Four, aquifers do not get filled up with sediments. Five, there is no reduction in the flows of the rivers downstream and the groundwater recharge. The disadvantage of aquifers is that farmers have to use electricity to pump out water from the earth whereas they are supplied flowing water through canals from storage dams. This cost also has a silver lining. Presently, farmers overuse canal water. The increased cost of water will be an incentive for them to use irrigation judiciously. They can be compensated for this increase in cost by a corresponding increase in the Minimum Support Price.
The cost of storing water in aquifers is also less than storing it in reservoirs. I have not seen a comparative study for India. However, a study for California by “Water in the West” estimated the cost of storage in aquifers at US Dollars 390 per acre-foot against USD 2200 for storing the same in reservoirs. The potential to store water in aquifers was estimated at about 1075 million acre-feet against surface storage from all the major reservoirs was less than 50 million acre-feet. The figures for India are somewhat similar. The storage capacity of our reservoirs is about 253 BCM. The Central Ground Water Board has estimated that 85 BCM water can be stored in groundwater aquifers from an area of 9.4 lakh square kilometers. The total area of India is 32.7 lakh square kilometers. The total groundwater storage potential would be much larger than the 85 BCM estimated above. I guesstimate 200 BCM. A former Chairman of CGWB has suggested that 1.1 crore artificial recharge structures need to be built at an expenditure of Rs 79,000 crores.
In the next step, the storage dams must be decommissioned and that water should also be stored in groundwater aquifers so that we can save the water being lost by evaporation, during transportation and due to less downstream recharge. We can prevent the loss of 40 percent of the 253 BCM capacity of reservoirs. 101 BCM additional water can thus be made available.
The Budget should provide a huge grant to reduce the loss from evaporation, to increase the artificial ground water recharge, to decommission reservoirs and store that water in aquifers.We can add 501 BCM to our water availability. The present extraction of groundwater is about 231 BCM per year and availability from reservoirs 253 BCM – 40 percent loss = 152 BCM. Total available is 383 BCM. The Budget must aim to add 501 BCM to this.
We also need to reduce the demand of water. Tamil Nadu is an example where the supply has been increased but the demand has increased even more leading to a huge shortage. Tamil Nadu ranks No 2 in watershed management and No 3 in augmentation of groundwater recharge in the country according to the Niti Ayog. However, it has the lowest rank among major states agricultural water use practices. Tamil Nadu has done well in capturing the rainwater but is yet in crisis because it has poor water use management.
Eighty-five percent of water in India is used in agriculture. The main problem is farmers do not have an incentive to use water judiciously. Farmers leave the bore wells on and running as long as the electricity is coming. They flood the fields with canal water repeatedly even though such flooding does not add much to the production. The solution is to move to volumetric pricing. Farmers must be required to pay for the volume of water used. The Union Government must increase the Minimum Support Price correspondingly so that additional burden is not imposed on the farmer. However, this is a state subject. Thus, the Union Government must tie aid to irrigation to the implementation of volumetric pricing by the States.
The Union Government must also make a stiff increase in the exports of water-guzzling crops. We exported 21 lakh tons of sugar so far in the current year, 5 lakh tons of red chili in 2017-18 and 17,000 tons of menthol in 2018-19. We are packing our scarce water in these crops and exporting our water. This must totally stop. WE must also devise ways to reduce cultivation of water-guzzling luxury crops like grapes.
(The author is formerly Professor of Economics at IIM Bengaluru)