In this essay we will discuss about the water resources of the world.
Water resources are sources of water that are useful or potentially useful to humans. Uses of water include agricultural, industrial, household, recreational and environmental activities. Fresh water is a renewable resource, yet the world’s supply of clean, fresh water is steadily decreasing.
Water demand already exceeds supply in many parts of the world and as the world population continues to rise, so too does the water demand. Water being a prime natural resource, a basic human need and a precious national asset, its use needs appropriate planning, development and management.
World oceans cover about three fourth of earth’s surface. According to the UN estimates, total amount of water on earth is about 1400 million cubic kilometers (M km3) which is enough to cover the earth with a layer of 3000 meters (m) depth.
However, the fresh water constitutes a very small proportion of this enormous quantity. About 3 per cent (2.7%) of the total water available on the earth is fresh water of which about 68.7 per cent lies frozen in polar regions and another 30.1 per cent is present as groundwater. The rest is available in lakes, rivers, atmosphere, moisture, soil and vegetation (Fig. 7.1).
About 110, 000 km3 precipitate annually on earth’s surface. Around 60 per cent (61,000 km3) evaporates directly back into the atmosphere, leaving 49,000 km3 flowing towards the sea. At present, only 3,400 km3 are withdrawn for use and annual water use per capita among different countries of the world varies from less than 50 m3 to more than 1,000 m3.
World water resources as reported by the Central Water Commission, Government of India have been summarised in Table 7.2.
The 2030 Water Resources Group formed in 2008 to provide insights into emerging worldwide water resources in its report ‘charting our water future’ issued in 2009 provided a candid fact based integrated assessment of the global water situation over the next two decades.
Globally, current withdrawals of about 4,500 km3 exceeded the availability of about 4,200 km3. By 2030, the demand is expected to increase to about 6,900 km3, with a slight drop in availability to 4,100 km3. Thus, by 2030, a global deficit of 40 per cent is forecast.
For India, the annual demand is expected to increase to almost 1,500 km3 against a projected availability of 744 km3, a deficit of 50 per cent. The report admits unavoidable uncertainties in these estimates. As an independent check, an alternative prospective merits consideration.