Water is fundamental for all kinds of development. Human development and well-being, industrial and economic development, energy production and agriculture all rely on the availability of (often abundant) water resources. However, there are distinct differences between sectors of society, their relationship to water and the future implications that changes in availability may have.
The 20th century witnessed a sixfold increase in human water use, while the population increased 'only' threefold (Cosgrove and Rijsberman, 2000; Gleick, 2003). It is not only direct human water use that influences the quantity of water; availability could also be indirectly affected through water quality deterioration due to increased pollution and deteriorated aquatic ecosystems (Koplin et al, 2002; Baresel and Destouni, 2005; Lindgren et al, 2007). Water use statistics, should be treated carefully as they may include large uncertainties. As an example, we currently do not know if groundwater provides only 25 per cent or as much as 40 per cent of the world's drinking water (UN, 2006). So, what is water used for?
Domestic water use (drinking, sanitation and societal services) accounts for approximately 8 per cent of global water use, though at the household level it varies considerably by one's living standard (UN, 2003). In 2000 nearly 1 billion urban dwellers lived in slums and had as little as 5 litres per day at their disposal, while nearby middle- or high-income households had between 50 to 150 litres per day (UN, 2006). In 2006, according to the latest Joint Monitoring Programme report, 884 million people lack access to safe drinking water (WHO and UNICEF, 2008). This is nothing less than a scandal.
Industry is a thirsty water consumer and accounts for some 22 per cent of total use (UN, 2006), but with great regional variation. In rich countries, industry can command as much as 59 per cent of the water while developing countries dedicate roughly 8 per cent of their available water. Global economic growth has and will continue to fuel an expansion of industrial water use from about
750 cubic kilometres per year in 1995 to an estimated 1170 cubic kilometres per year in 2025. In Asia, for example, water withdrawal is five times higher today than in 1950 (Shiklomanov, 2007).
Industry is also a major water polluter. Some 300 million to 500 million tonnes of heavy metals, solvents, toxic sludge and other wastes accumulate each year from industry, 80 per cent of which is produced in industrial countries, but as much as 70 per cent of which are dumped untreated into waters in developing countries (UN, 2006). Therefore, industrial water use should also include the amount of water degenerated due to pollution; statistics, however, are lacking.
Predicting industry's future water use is difficult. Technologies can cut water use dramatically (in some cases to zero); but clear economic and legal incentives need to promote such technologies. Which industries grow is also a critical factor due to differences in water use and pollution generation by sectors.
Energy production is also a major water issue. However, the linkages are not always obvious. Reservoirs would seem to be built for energy generation, but merely 25 per cent of the world's dams produce hydropower. Europe uses 75 per cent of its hydropower potential, while Africa has developed only 7 per cent, a figure so low that raising it is viewed by some to be a cornerstone of Africa's future development (UN, 2006). Still, only about 2.2 per cent of the total primary energy supply by source (in 2002) comes from hydropower, according to the International Energy Agency (IEA), and even if there is a dramatic increase in hydropower production, the overall share will remain marginal.
Water is also used as a coolant in energy production with little effect on quantity; but the quality and temperature of the water may be affected in the process. Increased water use, changes in runoff due to climate change and higher water temperatures may similarly decrease the cooling capacity of a specific water source. Such factors will have to be considered where massive energy development (including coal-powered plants) will need to use huge amounts of water in fast growing economies such as China and India.
A debate emerging in recent years has centred on the water needs for bioenergy production. A dramatic production increase could drastically alter future water use - and food production - scenarios. The energy section of the 2006 World Water Development Report (UN, 2006) barely addressed bioenergy and water linkages. With some estimating that as much additional water is needed to meet our bioenergy needs as to meet our food needs in the future, this issue will only grow in importance in the global water debate.
At 70 per cent of global water use, the thirstiest sector clearly is, and will remain, agriculture, which has tripled its irrigated area between 1950 and 2003 from 94 million to 277 million hectares (producing 60 per cent of the world's grain). This irrigation growth has tapered as water has become scarcer. Forty years ago, irrigated areas were expanding at an annual rate of 2.1 per cent; but the last five years show growth of only 0.4 per cent (FAO, 2006).
Agricultural water management has also seen dramatic changes since the 1950s. Advances in seed, fertilizer and pesticide technologies, and the ability to store, divert and pump surface and groundwater have spawned 'green revolutions' nationally. Dams, diversions and other infrastructure harnessed blue water (lake, river and groundwater) resources for farming, hydropower and flood protection. As a result, it is estimated that 60 per cent of the large river systems in the world have been moderately or strongly affected (MEA, 2005a). Since 1950, water withdrawals have tripled, although the resource has not been used or managed efficiently. Globally, food production has kept pace with a doubling of the world population, a yield increase due more to increased cropping intensities than to expansion into previously uncultivated areas (Molden, 2007).
Water use in agriculture, whether for livestock husbandry, aquaculture or crop production, has also affected water quality. Soil erosion, salinization, sedimentation, and nutrient and pesticide pollution have contributed to a decline in water quality in many of the world's river systems and coastal zones.
The net result of population growth, economic development and improved diets is a drastic increase in water use, thus increasing risks of competition. Agriculture, accustomed to receiving the lion's share of water, but often showing the lowest economic return per drop, is being pressured by industries, cities and ecosystems, which need water to maintain their productive yet often undervalued services (UN, 2006). However, the true costs of these advances are only starting to be known. 'The lack of appropriate and efficient water resources management in the agricultural, industrial and domestic sectors have all contributed to degradation of ecosystems (Molden, 2007). The Millennium Ecosystem Assessment (MEA, 2005a) stated that humans have changed ecosystems more rapidly and extensively than ever before in the last 50 years in order to meet our growing demands for food, freshwater, timber, fibre and fuel.
The main drivers for the degradation of freshwater ecosystems have been habitat alteration through wetland drainage and land-use change, alteration of river flows and pollution. Climate change is also expected to increase the pressure on freshwater ecosystems (UN, 2006). The withdrawal of water for human use, and particularly for irrigation, is contributing to a shift to environmentally stressed conditions in many river basins around the world (Smakhtin et al, 2004). There are an increasing number of cases around the world where rivers are no longer reaching the sea and groundwater tables are dropping as we are overusing our global freshwater by 5 to 25 per cent more than the long-term accessible supply allows. Much of this water is used for irrigation, with irretrievable losses in water-scarce regions, although overuse is everywhere (MEA, 2005b). Huge demands are also being made on coastal and freshwater ecosystems, where freshwater species are threatened by human activities. Species populations fell 50 per cent between 1970 and 2000, representing a sharper decline than measured in either terrestrial or marine biomes (UN, 2006)
All of these realities, all of these uses, all of these dependencies mean that effective water management must include both a multitude and a combination of options and approaches; there is no silver bullet to cope with water-related challenges.
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