REVIEW ARTICLE CURRENT SCIENCE, VOL. 86, NO. 9, 10 MAY 2004 1216 Water for India in 2050: first-order assessment of available options S. K. Gupta* and R. D. Deshpande Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India Water resources of India are examined in the context of the growing population and the national ambition to become and be seen as a developed nation. The moti- vation was provided by the continuing debate on the proposed project for interlinking of rivers by National Water Development Agency. The population of India is expected to stabilize around 1640 million by the year 2050. As a result, gross per capita water availability will decline from ~ 1820 m 3 / yr in 2001 to as low as ~ 1140 m 3 /yr in 2050. Total water requirement of the country for various activities around the year 2050 has been assessed to 1450 km 3 /yr. This is significantly more than the current estimate of uti- lizable water resource potential (1122 km 3 /yr) through conventional development strategies. Therefore, when compared with the availability of ~ 500 km 3 /yr at pre- sent, the water availability around 2050 needs to be almost trebled. Various options have been considered in quantitative terms, as possible sources to augment the anticipated deficit. It is argued that due to considerations of gestation period and capital requirements, rainwater harvesting and water-conservation measures must receive the highest priority followed by renovation and recycling to be followed by intra- and then inter-basin transfers in the last phase. But, investigations and planning pro- cesses for all options must begin immediately. WITH rapid population growth and rising expectation for a better life, the natural resources of our earth face in- creasing pressure. It is paramount that basic resources for human survival, viz. air, land and water must be properly managed. The quantity and quality of these resources are critical to ensure adequate food supplies, public health and transportation. In particular, the management of water re- sources has profound impact on society with regard to quality of life. Water-management decisions can have environmental, physical, social and economic impacts that are widespread and pervasive. It is, therefore, necessary to have most relevant information for arriving at rational decisions that will result in the maximum amount of benefit to most people. Accurate and reliable information on the water resource system can, therefore, be a vital aid to strategic management of the resource. To appreciate this, an over- view of the emerging water-resource scenario in India is presented in the following. Emerging scenario – water resources of India A gross annual assessment of available water resources of India 1 is given in Table 1. The Central Water Commission worked out the estimated utilizable surface water (EUSW) in each river basin. This is the quantum utilizable through conventional run-of-the-river schemes and storage reser- voirs and among other constraints depends on availability of suitable sites for construction of dams and diversion structures. Total utilizable surface flow in all river basins of the country 2 was thus estimated ~ 690 km 3 /yr. Further, a bare minimum live storage of 385 km 3 was estimated as needed to balance seasonal flows to achieve ~ 690 km 3 /yr EUSW for irrigation of 76 mha. Sedimentation in reser- voirs reduces utilizable resource. Replenishable groundwater (RGW) resource was esti- mated by the working groups (constituted in 1994–95) based on a large volume of hydro-geological and related data generated by Central Ground Water Board (CGWB) and the State groundwater organizations and the existing knowledge of groundwater regime 1 , as ~ 432 km 3 . The estimated RGW is the sum of natural recharge from rain- fall (342 km 3 ) and potential due to recharge augmentation from canal irrigation system (90 km 3 ). Water requirement is a derived quantity. The key deter- mining elements are the population and the desired quality of life. The latter depends on a large number of parameters *For correspondence. (e-mail: skgupta@prl.ernet.in) Table 1. National water resources of India at a glance Resource Quantity Precipitation (%) Annual precipitation (including snowfall) 4000 km 3 100 Evaporation + groundwater 2131 km 3 53.3 Average annual potential flow in rivers 1869 km 3 46.7 Per capita water availability (1997) 1967 m 3 – Estimated utilizable water resources 1122 km 3 28.1 Surface water (EUSW) 690 km 3 17.3 Replenishable groundwater (RGW) 432 km 3 * 10.8 1 km 3 = 10 9 m 3 = 1 billion cubic metre (BCM) = 0.10 million ha m. *Natural recharge from rainfall (~ 342.4 km 3 ) + potential due to aug- mentation from canal irrigation system (~ 89.5 km 3 ). Source: Ministry of Water Resources (MOWR) 1 .