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The demand for fresh water has continued to climb as the world's population and economic activity have expanded

—Aisha Shereen, Dr. R. Ansari 
and D. S.M. Alam
June 04 - 10, 2001

Most of the earth's 1.4 billion cubic kilometers (km3) of water is saline; 97 per cent forms the oceans. About 30 million km3 of the remaining fresh water is located in icecaps and glaciers, and a large portion of the 440 million km3 of groundwater remains essentially inaccessible. Thus, the supply of fresh water available for human use depends on the dynamics of the hydrological cycle, in which sea water evaporates and falls over land as precipitation. The renewable supply of water is defined as the surface water runoff from local precipitation, the inflow from other regions, and the groundwater recharge that replenishes aquifers. Each year, evaporation from the oceans yield about 453,000 km3 of the water to the atmosphere. Over 90 per cent returns to the oceans as precipitation. The approximate 41,000 km3 remaining is carried by winds to land, where it is combined with slightly more than 72,000 km3 of water evaporated from landmasses and fall as a precipitation. This gross continental precipitation (113,000 km3) creates enough water to cover the earth's land surface to a depth of 83 centimeters. The rainfall recharge soil moisture and groundwater that returns to the seas to complete the hydrological cycle. But, of this 41,000 km3, only about 14,000 km3 is available as a stable run-off, while the rest flows back to the sea as flood run-off. Of this, 14,000 km3 about 5000 km3 flows through unpopulated or sparsely populated areas like amazon river basin, leaving only 9000 km3 readily available for human use. Because water can, in principle, be reused many times, the availability of water for human use depends as much on how it is used and how water resources are managed as on any absolute limits.

Population variations in different regions of the world also affect the adequacy of per capita water availability. As with food, the problem is not one of the global shortage, but one of uneven distribution. Where water is plentiful, people are frequently few, and vice versa. Another determinant of water availability is the inter annual variability of rainfall. The area of highest variability, where rainfall varies more than 40 per cent over the long term average, are sub-Saharan Africa, southwestern Africa, Saudi Arabia, southern Iran, Pakistan, western India, southwestern United States and northwestern Mexico. The most water rich country in terms of runoff from rainfall to population is Iceland, with more than 500,000 m3 per person per year; the most water poor is Egypt, with just 0.02 m3. However, to sustain the quality of life as defined by most developed countries at least 30 m3 of water is required per year per person for domestic use. Domestic and recreational need accounts for only 6 per cent of the world's freshwater use.

Irrigated agriculture accounts for 73 per cent of the water used and industry accounts for the remaining 21 per cent. But this pattern varies from region to region according to the distribution of earths fresh water supply. Many countries are facing shortage of fresh water and approximately one third of humanity must cope with impure water. According to a report of United Nations this figure will be doubled within thirty years. The expanding demand is pushing beyond the sustainable yield of aquifers in many countries and draining some of the major rivers dry before they reach the sea.

There are several reasons to expect water shortage to grow worse in future.

i) Further increases in irrigated land are vital for the world food production to meet the requirement of growing populations.
ii) The growth in urban population of developing world will require a large increase in water supply.
iii) The normal method of increasing available water supplies, building more dams have graved environmental consequences, which are only just coming to be not fully appreciated.
iv) When rivers cross national borders, countries may grab what they can at their neighbour's expense. In the world, about 200 river basins are shared by at least two nations. India, Pakistan, Bangladesh and Egypt are the examples of some major countries sharing their water resources in such a situation when underground water sources are decreasing continuously.

Fortunately, many opportunities exist to improve the efficiency of water use for different purposes. Irrigation systems, for example, often perform poorly, wasting as much as 60 per cent of the total water pumped, before it reaches to the intended crop. Moreover, where drainage is poor, mismanaged irrigation waters are a major source of soil waterlogging and salination, which affect an estimated about 80 million to 110 million hectares of arable land worldwide. More efficient technologies including drip irrigation systems, lining of irrigation canals, more efficient sprinkles, and better irrigation timing and volume control are beginning to come into limited use in a few countries and have proved effective at reducing water use. Since agriculture is responsible for some 70 per cent of global water use, the potential for water savings through greater efficiency in irrigation is enormous. In some third world's countries, about 60 per cent of drinking water is wasted during impaired distribution system. Experience in developed nations also indicates that controlling industrial pollution has a secondary benefit of actually reducing the quantity of water used per unit of industrial output. Thus, pollution control offers one potent and cost-effective mesans of addressing urban water problems.

Despite improvements in the efficiency of water use in many developed countries, the demand for fresh water has continued to climb as the world's population and economic activity have expanded. Interestingly, from 1940 to 1990, withdrawals of fresh water from rivers, lakes, reservoirs, underground aquifers, and other sources increased by more than a factor of four. Increases in irrigation and, to a lesser extent, industrial uses of water have been the largest sources of this growing demand. Pumping water from underground aquifers faster than they can be recharged or diverting so much water from wetlands or rivers that freshwater ecosystems fail are clearly unsustainable practices. Examples of unsustainable water uses can be found in virtually every region in the depletion of the Ogallala aquifer in the United States and similar over-pumping of other aquifers in parts of North Africa, the Middle East, India, Pakistan and Southeast Asia; in the diversion of river water from the dying Aral Sea in Kazakhstan and Uzbekistan and from the Florida Everglades; that are causing intrusions of sea water into deltas and coastal aquifers, dropping of water table and land subsidence. If water supplies are finite and water use is rising, what can be said about future pressures on water supplies? In addition, given the enormous geographical variability in water resources, where might these pressures be most severe? One approach to answering these questions is the concept of a water stress index, measured as the annual renewable water resources per capita that are available to meet needs for agriculture, industry, and domestic use.

On the basis of the past experiences of moderately developed countries in arid zones, renewable freshwater resources of 1,000 cubic meters per capita per year have been proposed as an approximate benchmark below which most countries are likely to experience chronic water scarcity on a scale sufficient to impede development and harm human health. By this measure, some 20 countries already suffer from water scarcity. The water stress index can also provide a rough guide to future water scarcity. Population Action International has projected future water stress index figures for 149 countries using U.N population projections and holding renewable water resources constant. It projects that the number of people living in water-scarce countries will rise from 132 million in 1990 to between 653 million (with the low population growth projection) and 904 million (with the high population growth projection) in 2025. By 2050, the population projected to be living in water-scarce countries will rise to between 1.06 billion and 2.43 billion, representing roughly 13 to 20 per cent of the projected global population. Africa and parts of western Asia appear particularly vulnerable to increasing water scarcity, but the list of potentially affected countries includes nearly one third of those studied and includes countries in four of the five major continents. In addition, nations not included in the Index because overall they have adequate water resources may have arid regions where drought and restricted supplies are common. Such regions include northwestern China, western and southern India, large parts of Pakistan and Mexico, and the western coasts of the United States and South America. Thus, the actual population subject to water shortages might be even larger than these estimates.

Moreover, efficient management and modern technologies can stretch even scarce water supplies much further. Israel, for example, supports its population, its growing industrial base and intensive irrigation system with even less than 500 cubic meters per person per year. In the absence of significant changes in policy and far more effective management of water resources, this could pose serious long-term obstacles to sustainable development in many countries. In Pakistan, the water charges for irrigation are known to be low, ranging from Rs.50 for crops and vegetables to Rs.125 for orchards. According to an official statistics, the costs of irrigation water are highly subsidized in Pakistan. Some experts assert that these low rates for water are the main cause for irrigation mismanagement by the users, which results in the denial of water to the tail-end communities of the farming system. The issue of irrigation subsidies should be dealt with carefully, and no subsidies should be provided that result in inefficient agricultural use of water. The cost recovery should focus on the amount of irrigation water used, i.e., the benefit accrued, and on the drainage surplus created by the particular agriculture.

At the same time, contamination by pollutants has seriously degraded water quality in many rivers, lakes, and groundwater sources, effectively decreasing the supply of fresh water worldwide. The results have been increased tremendous pressure on freshwater resources in most regions of the world and lack of adequate supplies in some localities. Water experts and International Institutions have warned that water shortages could become critical in some regions, which could lead to a heightening of tensions between countries sharing the water resources of international rivers. Many Asian cities, where 56 per cent of the population will live by 2025, are ill-equipped to provide their growing populations the safe drinking water and sanitation they need. Upto one in four in the region lacks formal sanitation. The poor are most prone to diseases caused by unsafe drinking water and inadequate sanitation. Almost 250 million cases of water-borne diseases and about 10 million deaths are reported worldwide each year. About 9500 children die every day from lack of water or more frequently diseases caused by polluted water.

To feed the burgeoning world population (90 million people every year that passes), will increase the population pressure for water supplies most probably in the middle of the current century. Nearly half of the world population will have insufficient water. What happens between now and next 50 years will be of enormous importance for the future of human kind. This is the core issue for all. If we as individuals make sensible and humane decisions in the way we live, our daily lives then the societies in which we live will become more sensible and humane. This is an issue for all people, not just for the devour politicians. The more we can understand about the ways the world is changing, the greater the chances we have of securing its future in the years beyond. Greater public awareness is needed to help create the policies, strategies, and incentives to establish integrated water resource management on a global basis. Population control, land and water management and pollution control should be at least at our top priority to save and protect our future generations on the earth.