Technical
background
document
© FAO, 1996
1.1 It is a truism that water and land are the two primary resources for agriculture, indeed for all life on earth. Where the supply of water is adequate and soils are fertile, agriculture can sustain civilized human life – provided, of course, that the climate is favourable. Conversely, where water is insufficient, even temporarily, agriculture fails and food insecurity ensues. At a time when the world’s population and food needs are climbing by unprecedented amounts, it is becoming increasingly difficult to supply more water for farmers. With intensifying pressure on vulnerable water and land resources, the task of efficient management becomes vital and urgent.
1.2 Fresh water is a finite resource, widely but not everywhere available, sensitive to external influences and environmental degradation, difficult to manage as it is mobile under its own peculiar conditions, and costly to control and develop. Population growth and socio-economic development lead to increasing demands, while global change and international geopolitics are increasing uncertainties about water. Water is becoming scarce as its competing uses increase, and both the necessity and the motivation for its management will increase. Water scarcity threatens fundamental aspects of human security: food production, the health of the aquatic environment and social and political stability.
1.3 The problem of managing limited freshwater resources includes both quantity and quality aspects. While rivers are diverted from their natural courses and aquifers are overdrawn, and as streams, lakes, estuaries and aquifers are used to absorb the waste products of careless management, remaining useful water supplies are threatened with degradation. These ills have to be remedied. Depletion and degradation are not inevitable. The knowledge and the resources exist to feed humanity in a sustainable manner. The task is to mobilize the knowledge and the will to tackle what otherwise threatens to become a crisis.
1.4 While there are various policy options available for water management, water is a sensitive topic, and reform of public behaviour towards water is a difficult task with high political and administrative costs. Perfection may not be achievable and policy changes have long-term impacts and always result in gainers and losers. Therefore, even when the pay-offs are substantial, the change may not be acceptable to all parties affected.
1.5 Time is a constraint in the implementation of policy. Management measures need to be based on probable trends at global and local levels, such as population growth, urbanization, globalization, evolution of technology and information, shifting cultural influences and environmental degradation. Gaining acceptance of water policy and of the measures required to implement the policy is time consuming. Forces that drive or oppose such change need to be understood and allowed time to be accepted.
1.6 Agriculture is the major user of water, claiming more than two-thirds of the water withdrawn from the earth’s rivers, lakes and aquifers. As populations expand and economies grow, water becomes an increasingly scarce and valuable resource. Competition among agriculture, industry and cities for limited water supplies is already constraining development efforts in many countries. Paradoxically, however, even as water is becoming increasingly scarce, the use of water in too many areas is still highly inefficient. In some places, as much as 60 percent of the water diverted or pumped for irrigation does not reach the crop. Cities distribute water through leaky systems to underpaying or non-paying customers. Some losses are inevitable, but others are recoverable and reusable. Industries, cities and agriculture allow water to become polluted. Although some pollution is part of the very process of using the water, large amounts of water are lost to unrecoverable contamination.
1.7 Wasteful irrigation practices not only entail the loss of precious water but also cause waterlogging and salinization. More than 10 percent of the world’s irrigated land suffers from varying degrees of salinization, and the extent and severity of this phenomenon are growing. Surface-water quality is deteriorating because of the disposal of urban and industrial wastes as well as chemical residues from agriculture. Groundwater is not only polluted from surface sources; aquifers can also be irreversibly damaged through the intrusion of sea water. Also affected are aquatic ecosystems in streams and estuaries receiving water in inadequate quantity and quality.
1.8 Agriculture’s traditional primacy in the allocation of water resources is being questioned. Critics are calling upon governments and donors to rethink the economic, social and environmental implications of publicly funded and operated water-control projects. Despite large investments and subsidies, irrigation performance has not always fulfilled expectations for yield increases and efficiency of water use. Agriculture is not only the world’s largest water user in terms of volume, it is also a relatively low-value, low-efficiency and highly subsidized water user. As the limits of renewable fresh water that the hydrological cycle can yield are probed, this situation cannot be carried into the future.
1.9 Agriculture is often unable to compete economically for scarce water. As cities and industries can afford to pay more for water and earn a higher economic rate of return from a unit of water, the burden is upon agriculture to prove that its share of limited water supplies is applied to good advantage in ensuring food security. Otherwise, agriculture will be forced to give up more and more water for higher-value uses in cities and industries. The irony is that irrigated agriculture is expected to produce much more in the future while using less water than it uses now. The effect on future food production of the shift of water from agriculture to cities has not yet been fully assessed.
1.10 Food security is closely linked to water security. Between 30 and 40 percent of the world’s food comes from the irrigated 17 percent of the total cultivated land. Around one-fifth of the total value of fish production comes from freshwater aquaculture. Security and stability in food supplies in the next century will be closely linked to success in water control. Moisture control at root level allows for the maximization and stabilization of production by ensuring that fluctuations in the rainfall regime do not result in stress to the crop, thus fully realizing the benefits of high-yielding varieties and plant nutrition and protection systems. Success will not come merely from expansion (more rivers dammed, more canals built, larger tracts of land levelled and watered). Increasingly, it must come from improved management: rehabilitation of inefficient systems and substitution of traditional systems stemming from a past era of plenty for systems based on accurate technology. Achieving this will require on the one hand funds, and on the other, qualified, capable farmers and managers.
1.11 The World Food Summit provides an opportunity to reflect on the inextricable linkages between water resources and food security; to scrutinize how water for agriculture is managed at present; and to stimulate critical thinking, research and action for the future. All aspects of water resources – physical, economic and social – must be considered at this juncture.
Water: a limited resource
2.1 The large amounts of water contained in the sea, in the ice caps and glaciers of Antarctica and Greenland and deep in the
ground are not accessible for use in agriculture. Fresh water for human consumption and agriculture stems essentially from
rainfall over land. However, there can only be as much water precipitated from the atmosphere as is evaporated by
vegetation, from the land and from free water surfaces, including the seas. Water is continuously recycled as a result of
evaporation driven by solar energy, and rainfall and river flow are dependent on the annual cycle of the seasons.
2.2 The average annual rainfall over land amounts to 110 000 km3, of which some 70 000 km3 evaporates back into the atmosphere. The fraction of water evaporated is sometimes called green water, that is, the water supply for all non-irrigated vegetation, including forests and woodlands, grasslands and rain-fed crops. Of the green water, some 26 percent, or 18 000 km3, is already being used by people, mainly for agriculture, leaving 74 percent, or some 52 000 km3, to meet the water needs of all other land-based species and natural communities.
2.3 After discounting evaporation from continental rainfall, there remains an annual 40 000 km3 of fresh water in lakes, reservoirs, streams and aquifers in active exchange with surface water. This so-called blue water is unevenly distributed over space and time and is a transient presence while it flows to join a water sink such as the sea or a salt pan. While it remains on the surface, it is permanently eroded by evaporation. Not all of it is accessible: the remote flows of the Amazon, Zaire-Congo and undeveloped rivers in the far north, which are not where the water is in demand, amount to some 20 percent of total blue water. A large part of runoff is not available when it is needed and is hard to capture because it is floodwater (Figure 1)
Figure 1: ACCESIBLE BLUE WATER AS PART OF TOTAL ANNUAL PRECIPITATION ON LAND
2.4 Reliable flow realistically accessible for human use is estimated at 9 000 km3, to which 3 500 km3 of runoff regulated by existing reservoirs is added for a total current estimate of 12 500 km3 per year of runoff. Harnessing the remaining blue water (27 500 km3) to make it available where and when required is difficult and costly because of topography, remoteness from centres of population and development, and the social and environmental consequences of impoundment and other water development works.
2.5 Annual withdrawals for agriculture, industry, municipalities and reservoir losses amount to 4 430 km3, of which roughly 54 percent, or 2 285 km3, is actually consumed, while the remaining 46 percent is returned, albeit at a lower quality. Part of available surface water must be left to follow its natural course to ensure effluent dilution and safeguard conservation of the aquatic ecosystem. Exactly how much water needs to be left in a river will vary with the time of the year and many factors specific to each river basin. While a better understanding of the rivers’ complex ecological workings is pending, these instream flow needs are estimated at 2 350 km3. Water appropriated for human use, including withdrawals and instream flow needs, totals 6 780 km3 per year, that is, 54 percent of accessible runoff (Figure 2).1
Figure 2: PARTS OF GREEN WATER AND BLUE WATER ALREADY APPROPRIATED FOR HUMAN USE
2.6 Thus more than half of the easily accessible freshwater resources have already been subscribed. Taking into account demographic and water-demand projections, the global water figures point to a tightening water management situation. Because both water and population are unevenly distributed, a critical condition has already been reached in various countries and regions, while increasing areas of the world are suffering from freshwater shortages and competition between users is rising. The situation is analysed below as it relates to water per caput.
2.7 Agriculture has long accounted for the greater part of human water use and currently claims some 70 percent of world water withdrawals. Domestic, municipal and industrial uses account for the remaining 30 percent. Climate and economy influence the use given to the water withdrawn from natural courses. Thus industrial countries in humid, temperate regions use a smaller part of water for agriculture than do developing countries in the arid tropics; agriculture may claim more than 90 percent of water in arid developing countries and less than 30 percent in humid temperate industrial countries. The pattern of water use can serve as an indicator of development: as wealth increases, water withdrawal shifts from agriculture to industry and the domestic sector.
2.8 By far the largest part of agricultural water withdrawals goes to irrigation of roughly 250 million hectares worldwide. Water effectively used for production is evaporated in the biological process of producing the crop. Water abstracted for irrigation but, for various reasons, not taken up by the crop for the most part emerges as tailwater (drainage) and as groundwater recharge. Irrigation has an impact on the quality of water mobilized but not consumed through increased saline concentration as well as contamination from excess fertilizers and pesticides.
2.9 Global estimates indicate that irrigated agriculture globally produces nearly 40 percent of food and agricultural commodities on 17 percent of agricultural land, thus making irrigated areas disproportionately important to global food security. Water-control technology achieves this remarkable productivity boost in a variety of ways. Generally, irrigation provides adequate water supply to plants during the entire growing season, thus facilitating high yields. In the tropics and where the climate is adequate, water control can secure a second and sometimes a third crop in a year, if sufficient water is available. In humid regions, irrigated agriculture only supplements soil moisture provided by rainfall. Depending on climate, crops and cropping intensity, irrigation uses from 2 000 to 20 000 m3 per hectare annually. Subject to large variations according to climate and season, it can be roughly estimated that blue water accounts for one-half of moisture effectively taken up by crops. This is an estimate of the global average; in very arid regions, all the soil moisture taken up by the crop is supplied by irrigation.
2.10 Water cannot be substituted in biological production processes. In California, United States, for example, producing wheat requires 1.3 m3/kg, soybean oil 22 m3/kg, beef 16 m3/kg and poultry 5.8 m3/kg. These figures can change somewhat depending on climate and production methods in various regions of production. Producing a typical California diet requires about 2 200 m3 per person per year, of which 64 percent is used in meat production. The corresponding figures for Tunisia are 1 100 m3 per person per year, of which 27 percent is for meat. In California, the amount of water input met by irrigation was estimated at over 70 percent, while in Tunisia it was close to 60 percent. Of course, many regions, including the two mentioned as examples, import and export food and consequently the water that it carries2
2.11 Accessible blue water, 50 percent of which is already globally committed, cannot be replaced in some of its functions: as drinking-water for humans and animals, for hygiene, washing, sanitation and municipal use, for industrial processes and for fish, aquatic life and the environment. For this reason, it has a higher scarcity value than green water, and its application is most efficient in supplementing soil moisture when rain is insufficient or fails. Wherever water is scarce, efforts will be aimed at harvesting and bringing to roots a larger share of rainfall to save blue water with a higher scarcity value.
WATER SITUATION BY REGIONS AND COUNTRIES
2.12 Table 1 shows that one-third of all continental runoff is produced by Asia. However, in terms of specific discharge (runoff by km2), South America is seen to be better endowed with water than other continents. These overall figures, which are averages over large areas including very humid regions and deserts, can be misleading. Thus, the disaggregation of Oceania from Australia shows that the latter continent is very poorly endowed, while Indonesia, for example, has plenty of water. The trend in the evolution of water resources per caput from 1960 to 2000 reflects demographic growth. Asia, Europe and Africa are approaching water scarcity. The situation in Europe, however, is fairly stable, while Africa now has only about one-third of the per caput water it had in 1960. In major Asian countries, water available per individual is now close to a biologically significant figure: the amount of water (in the form of soil moisture) required to produce the annual per caput diet (roughly 2 000 m3). In China, with 2 300 m3 per person per year, irrigated agriculture currently contributes to about 70 percent of food production, while in India, with 2 000 m3 per caput per year, irrigation contributes more than half the total.
2.13 The averaged figures of Table 1 cannot show the critical situations known to exist in particular in North Africa and the Near East. Table 2 lists a selection of countries expected to have low water availability per caput by the year 2000 and therefore facing, or liable to face, a critical water management situation. For some of these countries, the water available is generated inside national borders; other countries, however, depend heavily on transboundary river flows. The list is not complete, and a number of other countries have very small per caput water availability. Moreover, some countries with a good average still have regions where water availability is poor. The water crisis is not covering the globe all at once but is gradually reaching arid and very densely populated regions.
Table 1: DISTRIBUTION OF WATER RESOURCES BY CONTINENT
2.14 Table 3 contains water-use figures by continent, net of river inflow requirements and reservoir evaporation. It shows that, as already stated above, agriculture represents more than two-thirds of world water use. Agriculture, however, uses more than 85 percent in Africa and Asia but only 33 percent in Europe; indeed, in the small, industrialized continent more than 50 percent of water is used in the industrial sector. Water use per person is highest in North America, reflecting the large-scale agricultural and industrial development in this region. At the other end of the spectrum, water use per caput is lowest in Africa, where the water management infrastructure is underdeveloped and the resource has not been mobilized.
2.15 The term water scarcity describes a situation where users are in competition for access to water. Human interventions bring about water scarcity through population growth, misuse and inequitable access. Population growth contributes to scarcity simply because the available water supply must be divided among an increasing number of people. Human activities also bring about water scarcity by contaminating existing supplies, thus making them unusable. Overused aquifers require pumping from ever greater depths at increasing cost, while saltwater intrusion may disable the aquifer itself. A shift in access or distribution patterns may concentrate water resources among one group and subject others to extreme scarcity. For example, large numbers of urban poor pay much higher prices and a much larger share of their income for water than families with access to a city water system.
2.16 Under conditions of water scarcity, agriculture is in competition for limited supplies with other users, such as urban and municipal water supplies and industry, that have a higher potential and economic weight. Adapting to a situation of increasing water scarcity and increasing reliance on trade for food security can be difficult in traditional rural societies. The process of converting rural societies to new patterns of economic and social activity requires time, sometimes several generations. For many countries that are approaching or are already suffering from water scarcity, time is at a premium for development of policy and strategy as well as for building the appropriate institutional and legal framework and the required management capacity.
Table 2: COUNTRIES PREDICTED TO HAVE SCARCE WATER RESOURCES IN THE YEAR 2000
Table 3: WATER USE BY CONTINENT (1990)
2.17 Management of water resources to cope with scarcity requires recognizing how the overall water sector is linked to the national economy. Equally important is understanding how alternative economic policy instruments influence water across economic sectors as well as among local, regional and national levels and among households, farms and manufacturers. Macroeconomic policies and sectoral policies that are not aimed specifically at the water sector can have a strategic impact on resource allocation and aggregate demand in the economy.
2.18 Action on water scarcity is basically constrained: there is not only limited time to act to meet growing water needs, but there are few measures available to produce more usable water, and there is increasing competition for funds to support measures. The insufficiency of current solutions results in precious time and resources being lost to provide the needed water. Information, development of awareness and intervention at the global and international level may not be effective, as it is only when water problems and conflicts appear at the country and local level that political, economic and environmental lobbies act to correct unsustainable current practices and to develop the potential for future supplies.
2.19 Water management policy needs to address a multitude of issues, such as:
2.20 The natural water management unit is the river basin. The sources of water in a basin are current and stored past precipitation (snow, ice and surface and subsurface storage in reservoirs, lakes, soil profile and aquifers); transbasin diversions from water-surplus to water-scarce basins; and desalinated water. The sinks where water becomes unavailable are: cession of water to the atmosphere in the form of vapour (evaporation and evapotranspiration); water salinization by mixing into a saltwater body (oceans, salt lakes and saline aquifers); and water pollution by salts and toxic elements that make it unusable.
2.21 Water abstracted from a river basin, in most cases returns after use, partially or totally, into the surface or underground water system where it becomes a secondary source of supply. The quality of secondary supply of drainage water is always lower than that of the primary water supply because water picks up pollutants as it is used, and because the consumptive use (evaporation) of water concentrates the salts that were in the input water. Thus, as water is progressively recycled through several stages in the basin, the amount and concentration of pollutants in the water increase substantially. Because of the complexity of the process, total water storage and abstraction figures can be misleading.
2.22 The opportunities for water efficiency gains at the level of the river basin are related to close management of the transit of water to water sinks. Some of the management aims are:
Box 1 |
| Desalination is an expensive option, largely because it is energy intensive. The best desalination plants currently operating use about 30 times the theoretical minimum energy requirement to remove salt from water. Technological improvements might reduce energy needs to 10 times the theoretical minimum, but this is still a substantial energy requirement. For the foreseeable future, desalination is likely to continue to be used primarily to meet drinking-water needs in water-scarce, energy-rich countries. |
2.23 Increasing irrigation efficiency, the percentage of the water abstracted that is taken up by the roots of the crop, does not necessarily increase the amount of water available in the river basin. Groundwater and drainage water stemming from established low-cost, low-efficiency irrigation is likely to be a water source for downstream users. Basin-wide water-use efficiency is raised when unproductive evaporation is reduced and when fresh water is prevented from mixing with salt water, for example, by storing floodwater in a reservoir until it can be used (Frederiksen, 1996; Appelgren and Klohn, 1996).
2.24 Groundwater plays an important role in water-resource management. This is often overlooked in the traditional way of assessing water resources through river runoff. One-third of river flow emerges from groundwater aquifers, and this represents the most stable component of surface flow. In arid and semi-arid areas, where aquifers are not always or are simply connected to the river network and where surface water is rare and unevenly distributed, groundwater may provide a source of water. Groundwater generally serves as a buffer against seasonal shortfalls in rainfall. It is in this role, for example, that groundwater helps to insulate the agricultural economy of the North Indian subcontinent from fluctuations in the monsoon climate. However, some of the most important food-producing regions are currently overpumping groundwater and depleting aquifers. The current trend shows that this is the case in most arid areas (e.g. in Asia, Mexico, the Near East, North Africa and the western United States).
2.25 A user (a farmer, for example) cannot indefinitely pump an aquifer faster than it is replenished. As the water table drops, the resource becomes too costly to continue pumping or too salty to irrigate crops, or runs out altogether. When the use of groundwater exceeds natural recharge, it means that the current level of water use is unsustainable and cannot be counted as reliable over the long term. Besides depleting supplies, groundwater mining can lead to other irreversible effects. Overpumping of groundwater in coastal areas can cause salt water to invade freshwater aquifers, contaminating supplies and spoiling the underground reservoir itself. In some cases, groundwater depletion can, through geological compaction, permanently reduce the aquifer’s natural capacity to store water.
2.26 Aquifer contamination is a growing problem worldwide, in particular for urban supply. Once pollutants such as nitrates from agriculture or toxic chemicals from industry penetrate the groundwater reservoir, they continue contaminating fresh water stored in it. Restoring a contaminated aquifer to safe conditions may take a very long time.
FOOD SECURITY AND WATER SECURITY
2.27 Food security is defined as a situation in which all households have both physical and economic access to adequate food for all members and where households are not at risk of losing such access. Ultimately, the principal determinant of food security is the purchasing power of the individual or household unit. Food security at the national level is achieved through the pursuit of food self-reliance, meeting food needs through an optimal combination of domestic supplies and of the opportunities of international trade.
2.28 In most countries situated in the arid regions, water availability per caput is already below the level that would allow enough food to be grown locally to feed the population. In some such countries, policy calls for enough food to be produced locally to protect against the contingency that they might be unable to import food at any cost, as in time of war or embargo. These policies have resulted in some cases in the exploitation of fossil water, a non-renewable resource, for the production of low-value food crops. It also generally results in domestic food production at a higher cost than international markets, thus decreasing the food security of the lower-income sector of the population. National anxiety about having enough water for food production is also among the driving forces behind so-called water wars.
2.29 Food self-reliance requires an economy that generates enough exports to cover the cost of the food imports necessary to meet the food needs of the population. It also requires that somewhere in the world the water be available to grow enough food for the entire population of the world. Reliance on trade has some perceived risks, such as deteriorating terms of exchange on world markets, uncertainty of supplies and price instability.
2.30 In the context of food self-reliance, water security is obtained through a policy of economic development and rational, sustainable use of the limited water resources. The aim of such policy is to meet the needs of domestic and urban users, as well as to supply the water needed by commerce, tourism and industry, so as to be able to provide employment opportunities to the population. Indeed, lack of water or irregular supply to urban areas leads to social unrest, political tension and water insecurity.
2.31 Efforts have been made to quantify minimum water needs compatible with water security. In the Near East, a minimum water requirement of 125 m3 per person per year has been proposed. It is composed of a minimum amount of water meant to cover domestic, urban and industrial use at 100 m3 per person per year, to which a small allocation of 25 m3 per person per year is added to allow for minimal growing of fresh vegetables, livestock and poultry (Shuval, 1996). Taking into account that some 65 percent of the water supplied for domestic, urban and industrial use can be recycled for agriculture or other industrial or urban non-potable uses, the total effective availability of fresh and recycled water under minimum water requirement conditions could reach 190 m3 per person per year.3
WATER POLICY REVIEW AND INSTITUTIONAL CHANGES
2.32 In a world of water scarcity, it is not possible to ignore the complexities of the natural world, human equity, concern about other species and the welfare of future generations. A statement of principles emerged from ICWE and served as the foundation for the water chapter of the global action plan developed at the 1992 United Nations Conference on Environment and Development (UNCED), Rio de Janeiro, Brazil. In 1993, the World Bank published a water-resources policy paper that establishes a framework for water management (World Bank, 1993b). All these documents call for recognition of the links between economic development and protection of natural ecosystems, for water to be recognized as an economic good, and for planning of water use and development to involve the public. Many countries have since initiated a process of review and reform of water-resources policy (FAO, 1995d; FAO/UNDP, 1995).
2.33 Institutions set the rules of the game within which the economic system operates. Property rights, for example, are part of an institutional arrangement governing economic activities including water use. The form of water institutions is significantly influenced by the relative scarcity of water and the transaction costs required to establish and enforce water rights. Water scarcity depends on both supply and demand. Transaction costs include the resources required to obtain information, negotiate agreements or property rights and police these agreements. Water supply and demand characteristics make transaction costs for water relatively high and the value of water relatively low compared with other resources or commodities.
2.34 Establishing an institutional structure for allocating water is a fundamental role of social policy for any nation. The choice of structure is ultimately a compromise between the physical nature of the resource, human reactions to policies and competing social objectives. Not surprisingly, different cultures make trade-offs based on the relative importance of their particular objectives. Countries try various means to balance economic efficiency (obtaining the highest economic value of output from a given resource base) and fairness (assuring equal treatment). Individual freedom, equity, popular participation, local control and orderly conflict resolution are other important objectives which societies must juggle when choosing a structure for water allocation. This process is very much under way and is actively supported by FAO, the World Bank and various donors (see FAO, 1995d; FAO/UNDP, 1995).
2.35 A large part of the world’s freshwater supplies are located within basins and aquifers that cross international borders. More than 200 rivers flow through two or more nations with political borders that cut across watersheds. A threat to human security arises from competition for water within and between countries as supplies fall short of needs, whether actual or perceived. At a time when much of the world has entered a zero-sum game with restricted or no possibilities of increasing overall supplies, satisfaction of competing users’ requirements must be sought in a broad context of development and security.
2.36 At present, international law offers little concrete help in resolving water conflicts since no legal framework governs the allocation and use of international waters, nor does it recognize the beneficial use of water for ecosystems. The International Law Association (ILA) and the United Nations International Law Commission (ILC) have put forward a number of principles, including four obligations: to inform and consult with water-sharing neighbours before taking actions that may affect them; to exchange hydrologic data regularly; to avoid causing substantial harm to other water users; and to allocate water from a transboundary river basin reasonably and equitably. In reality, these principles offer insufficient practical guidance. In particular, what constitutes reasonable and equitable is open to widely differing interpretations.
2.37 Among the factors that pose problems for efficient and equitable allocation and management of water resources are the variability and uncertainty of supplies, the complex interdependencies among users and the increasing scarcity and rising cost of water. There are clear incentives for individuals and countries to capture and use the resource before it flows beyond their control, that is, to build reservoirs upstream of the border. At the same time, there is little incentive to conserve and protect supplies for downstream users. To overcome conflict, sights have to be set wider to address the ultimate purposes for which control of water is desired: securing economic development, food security, health and the preservation of ecosystems, among other aims.
2.38 Water sharing and prevention of conflict depend on treaties among countries that are riparian to the same river. However, few treaties exist that include all countries within the river basin. Among river basins and regions recognized as hot spots are the Jordan, the Euphrates, the Nile, the Ganges and the Aral Sea tributaries. At the request of governments, FAO provides its interdisciplinary expertise in water-resources management, catchment protection, inland fisheries, policy, water law and institutions to work quietly towards finding what can be accepted as reasonable and equitable by the parties concerned.
(1) The global water balance figures were revised recently by Shiklomanov (1996), with minor adjustments that do
not change the overall picture. The meaning of reservoir capacity figures is dependent on the way the reservoir
performs. For example, if the large storage capacity of Lake Victoria is added to storage capacity existing in
Africa, the wrong impression is created that this continent is well supplied with water storage infrastructure. The
instream flow requirements, discussed in Chapter 7 of this paper, were elaborated according to Postel, Daily and
Ehrlich (1996), with reference to a minimum dilution requirement for untreated waste water of 28.3 litres per
second per 1 000 persons, amounting roughly to 1 000 m3 per person per year. Back to text
(2) The subject of water inputs required for food production was examined by Barthelemy (1993) on the basis of
data from California, United States, Egypt and Tunisia. The amount of water required to grow various crops (m3/t)
was used to determine the amount of water required to grow the diet of one person for one year: about 2 200 m3 in
California (diet rich in meat) and 1 100 m3 in Tunisia (diet low in meat). The water required to grow food, however,
comes partly from rain-fed and partly from irrigated agriculture. The part that comes from irrigated agriculture is
in turn partially derived from rain-fed soil moisture and in part from soil moisture supplied by irrigation water.
Back to text
(3) The concepts of food security, water security and water stress and the minimum water requirement are
discussed by Shuval (1996) in the context of Israel and the Near East region. Shuval suggests that 125 m3 per
person per year is enough to allow a community to prosper and live comfortably. Back to text
