International indicators for comparing water resources potential

Some of the definitions used to quantify and compare water resource potential internationally are as follows:

·         Internal Renewable Water Resources (IRWR): Internal Renewable Water Resources are the surface water produced internally, i.e., within a country. It is that part of the water resources generated from endogenous precipitation. It is the sum of the surface runoff and groundwater recharge occurring inside the countries' borders. Care is taken strictly to avoid double counting of their common part. The IRWR figures are the only water resources figures that can be added up for regional assessment and they are being used for this purpose.

·         Surface water produced internally: Total surface water produced internally includes the average annual flow of rivers generated from endogenous precipitation (precipitation occurring within a country's borders). It is the amount of water produced within the boundary of a country, due to precipitation. Natural incoming flow originating from outside a country’s borders is not included in the total

·         Groundwater recharge: The recuperation of groundwater is called the groundwater recharge. This is requisite to increase the groundwater table elevation. This can be done by many artificial techniques, say, by constructing a detention dam called a water spreading dam or a dike, to store the flood waters and allow for subsequent seepage of water into the soil, so as to increase the groundwater table. It can also be done by the method of rainwater harvesting in small scale, even at individual houses. The groundwater recharge volume is 418.5 cubic km and the per capita annual volume of groundwater recharge is 412.9 cubic m per person.

·         Overlap: It is the amount of water quantity, coinciding between the surface water produced internally and the ground water produced internally within a country, in the calculation of the Total Internal Renewable Water Resources of the country. Hence, Overlap = Total IRWR- (Surface water produced internally + ground water produced internally). The overlap for Indian water resources is 380 cubic km.

·         Total internal Renewable Water Resources: The Total Internal Renewable Water Resources are the sum of IRWR and incoming flow originating outside the countries' borders. The total renewable water resources of India are 1260.5 cubic km.

·         Per capita Internal Renewable Water Resources: The Per capita annual average of Internal Renewable Water Resources is the amount of average IRWR, per capita, per annum. For India, the Per capita Internal Renewable Water Resources are 1243.6 cubic m.

·         Net renewable water resources: The total natural renewable water resources of India are estimated at 1907.8 cubic km per annum, whereas the total actual renewable water resources of India are 1896.7 cubic km.

·         Per capita natural water resources: The present per capita availability of natural water, per annum is 1820 cubic m, which is likely to fall to 1341 cubic m, by 2025.

·         Annual water withdrawal: The total amount of water withdrawn from the water resources of the country is termed the annual water withdrawal. In India, it amounts 500000 to million cubic m.

·         Per capita annual water withdrawal: It is the amount of water withdrawn from the water resources of the country, for various purposes. The per capita annual total water withdrawal in India is 592 cubic m per person.