The annual precipitation including snowfall in India is about 4000 billion cubic meter (bcm) and the natural run off in the rivers is computed to be about 1869 bcm. The utilisable surface water and replenishable ground water resources are of the order of 690 bcm and 433 bcm, respectively. Thus, the total fresh water resources available for various uses, on an annual basis, are 1123 bcm. Although the per capita availability of water in India is about 1869 cubic meters as in 1997 against the benchmark value of 1000 cubic meters signifying ‘water-starved’ conditions, there is wide disparity in basin wise water availability due to uneven rainfall and varying population density in the country. The availability is as high as 14057 cubic meters per capita in Brahmaputra/Barak Basin and as low as 307 cubic meters in Sabarmati basin. Many other basins like Mahi, Tapi, Pennar are already water stressed.
Increasing demand of fresh water for various uses amid concerns of its decreasing availability is a major challenge facing planners, policy makers and water users world over. Withdrawal of ground water from aquifers in excess of their natural replenishment over the years have resulted in various adverse environmental impacts including drying up of shallow wells, long term decline of water levels and increased energy consumption for lifting water from progressively deeper levels. Excessive ground water development has also resulted in deterioration of ground water quality in coastal areas due to saline water ingress. Ground water development, therefore, needs to be regulated and augmented through suitable measures to provide sustainability and protection. Dependence on use of ground water for agriculture in events of monsoon failures is accelerating ground water depletion. In order to tackle the burgeoning problem of water level decline, it is necessary to take up schemes for water conservation and artificial recharge to ground water on priority.
Contamination of ground and surface water resources due to natural and anthropogenic pollutants has also emerged as a major challenge for sustainable ground water management in the country. Presence of naturally occurring arsenic, fluoride and iron in ground water in excess of permissible limits recommended for human consumption prohibits its use for drinking purposes in several states of India. Research and development studies need to be taken up for finding cost effective solutions to this problem. Dilution of pollutant concentration through ground water recharge can be one of the effective ways to mitigate the hazards of high concentration of these constituents. It is also desirable that rural water supply schemes be formulated and arrangements made to utilise fluoride/arsenic rich water for purposes other than drinking. Surveillance studies to determine the type and migration of pollution and measures for its control have become an absolute necessity from the point of view of long term sustainability of ground water resources. Purpose driven studies need to be undertaken to find suitable mitigation measures to combat this problem.
The water resources of the country play a major role in agriculture, hydropower generation, livestock production, industrial activities, forestry, fisheries, navigation, recreational activities, etc. According to National Water Policy in the planning and operation of systems, water allocation priorities should be broadly defined as; drinking water, irrigation, hydropower, ecology, agro-industries and non industries and navigation.
Surface Water Resources
The National Commission for Integrated Water Resources Development estimated the basin wise average annual flow in Indian river systems as 1953 km3. Utilisable fresh water resource is the quantum of withdrawable water from its place of natural occurrence. Within the limitations of physiographic conditions and socio-political environment, legal and constitutional constraints and the technology of development available at present, utilisable quantity of fresh water from the surface flow has been assessed by various authorities differently. The utilisable annual surface water of the country is 690 km3.
Ground Water Resources
In general, ground water available below the ground is comparatively fresh and potable due to natural filtration of rain water in soil before joining the ground water reservoir. Further, the ground water available in the upper phreatic zone is replenished every year through rainfall and other sources and hence the chances of contamination are relatively less. As per the latest estimates, the annual replenishable ground water resource for the entire country has been assessed to the tune of 433 bcm. The ground water assessed is the dynamic resource, which is replenished each year. The replenishable ground water resource is contributed by – rainfall and other sources that include canal seepage, return flow from irrigation, seepage from water bodies and artificial recharge due to water conservation structures. The overall contribution of rainfall to country’s annual replenishable ground water resource is about 67 per cent and the share of all other sources taken together is 33 per cent. Southwest monsoon being the most prevalent contributor of rainfall in the country, about 73 per cent of country’s ground water is replenished during the Kharif period of cultivation.
Keeping aside 34 bcm for natural discharge contributing to the river flow in lean season, the net ground water available for utilisation for the entire country is 399 bcm. The Annual Ground Water Draft is about 231 bcm. An analysis of ground water draft figures indicates that Chhattisgarh, Delhi, Goa, Himachal Pradesh, Jammu and Kashmir, Jharkhand, Kerala, Orissa, Sikkim, north eastern states of Manipur, Meghalaya, Mizoram, Nagaland and Tripura; and UTs of Dadra and Nagar Haveli, Daman and Diu, Lakshadweep and Puducherry, ground water draft for domestic and industrial purposes are more than 15 per cent which is comparatively higher than the national percentage of 8 per cent. In general, the irrigation sector remains the main consumer of ground water (92 per cent of total annual ground water draft for all uses).
In addition to the resources available in the zone of water level fluctuation, extensive ground water resources have been proven to occur in the confined aquifers in the Ganga-Brahmaputra alluvial plains, coastal areas and deltaic tracts. These aquifers have their recharge zones in the upper reaches of the basins. The resources in these deep-seated aquifers are termed ‘in-storage ground water resources’. In alluvial areas, these resources are normally renewable over long periods of time, except in cases like the ‘Lathi’ aquifers in Rajasthan, which comprise essentially non-renewable fossil water. Tentative estimates of the total quantum of in-storage ground water resources is about 10,800 bcm.
Need for Integrated Water Management
The problems being faced by the water sector in India demand a holistic look at the issue of management of surface and ground water resources. This is important as these two are interdependent and any management activity in the surface water sector is bound to affect the ground water sector and vice versa. Scientific management of water resources of our country calls for a judicious mix of various supply and demand side management interventions. Issues to be addressed in this context in the surface water sector will include flood control, irrigation management, improving water use efficiency, inter linking of rivers etc. As far as ground water resources are concerned, augmentation of resources, especially in over exploited and critical areas, through suitable techniques of artificial recharge techniques to utilise surplus run off available is of the highest priority. A nationwide rainwater harvesting and artificial recharge programme will help in augment ground water availability, ensure better distribution of water resources, enable flood control moderation, reduce soil erosion and increase storage capacity. This would involve accelerated programme of watershed development and rainwater harvesting and also provide incentives for rainwater harvesting in urban areas, making it mandatory for
large buildings. Other strategies such as conjunctive management of available resources, pricing and regulation, water conservation etc., are also important in this regard. Issues related to water quality also need to be addressed. Research and development initiatives, capacity building among various stakeholders and creation of awareness among the masses could also help initiatives for sustainable water management to a considerable extent. Such a holistic approach is possible only through the concerted efforts of planners, policy makers, administrators, scientists and the water users themselves.