Access to enough water of sufficient quality is fundamental for all human, animal, and plant life as well as for most economic activity. At the global level, plenty of water is available. But to meet the demand, water has to be supplied where and when it is needed. These spatial, temporal, and qualitative characteristics pose the greatest challenge to meeting the rising demand in all sectors. Water withdrawals are only part of the picture. Almost all uses put something back into the water that degrades it for other users. Water quality and competition between users are therefore critical issues for the future of water use. There is no single "magic bullet" to solve these complex and interrelated problems. Increases in water supplies, and especially storage, are needed, but so is demand management, including not only economic instruments but also education and other efforts to change behavior. Appropriate technologies and institutions must both play a role.
Throughout history, farmers and nations have depended on irrigation to produce sufficient, stable food supplies. Today, an estimated 40 percent of agricultural products and 60 percent of the world's grain are grown on irrigated land. Irrigation accounts for around 70 percent of water withdrawals world-wide and over 90 percent in low-income developing countries. But water constraints may make expanding irrigation to feed an additional 1.5 billion people by 2025 impossible. Access to clean water for drinking, cooking, bathing, and other household needs is fundamental, but over 1 billion people still lack safe domestic water supplies, and 2.4 billion lack adequate sanitation. Compared to other uses, the volume of water required for basic domestic needs is not great; municipal and industrial demands are growing much faster. By 2025, urban populations are expected to grow by over 2 billion, posing additional challenges for municipal water supply. While water quantity is not a major constraint on domestic use, chemical and biological contamination threatens the quality of water for human consumption.
Water is the source of life and livelihoods. Water also sustains natural ecosystems. Excessive human water withdrawals and pollution have disrupted many vital habitats and species, leading to calls to reduce water withdrawals and reserve water for nature. Yet most economic activities require water. Factories need water for processing, cooling, and waste disposal. In the last 50 years, agricultural water consumption doubled, but industrial consumption increased six-fold worldwide, and even more rapid increases in industrial use are expected.
The competition for water among domestic use, agriculture, industry, and nature is leading to scarcity even in areas that seemed water-abundant. Two ways of dealing with scarcity are to increase supply and limit demand. We examine each of these in turn.
Many countries have sufficient water to meet demands for all uses. However, much of the rainfall and river flows are highly seasonal, so there is excess at some times and not enough at others. Domestic and industrial uses require water every day, and demands may be even higher in the dry season. Agriculture can accommodate seasonal flows of water, but irrigated production in the dry season is often the most productive and profitable type of farming.
Storage is the key constraint to providing water in dry periods, when demands are highest and supplies lowest. Dams, groundwater aquifers, and small-scale water harvesting provide water storage. Dams have received the greatest investment, especially in the last 50 years. However, dams have become increasingly expensive in financial, environmental, and political terms. As the best sites are used up, the environmental costs of submerging forests and wildlife and the loss of land and livelihoods for those who are flooded out have given rise to organized political opposition.
Groundwater is a major source of stored water for irrigation as well as for rural and urban domestic use. Heavy withdrawal has led to falling water tables in many areas, limiting the potential for expanding groundwater use without more recharge of aquifers. Furthermore, arsenic, fluoride, salinity, and other aquifer contaminants have become serious problems for those relying on groundwater.
As the limitations of larger-scale storage in reservoirs and aquifers have become apparent, there has been renewed interest in smaller-scale water harvesting. Although small, water-harvesting structures can collect considerable volumes of water for storage above ground or in soil profiles. However, water harvesting can be expensive per unit of water, and is unlikely to be able to meet rapidly growing water demands.
Other options to increase supply include interbasin transfers and nonconventional sources. Interbasin transfers bring water from areas of abundance to those of scarcity, but they share many of the financial and environmental problems of dams. Desalination is expensive and energy-intensive, and hence has limited application at present. Other types of recycled wastewater can be used for some purposes. Urban waste-water is used for peri-urban irrigation in many areas, but the financial costs of treating sewage and the health costs of using water with fecal contamination and heavy metals call for caution in relying too heavily on such recycling.
Overcoming water scarcity requires using all options to increase available water supply and storage capacity, but supply options face serious financial and environmental constraints. We need to look to managing demand as the other half of addressing scarcity problems.
Economic measures such as pricing and water markets often receive the most attention in demand management. Water pricing is promoted as a means to recover the costs of building and operating water control structures. Water prices can also create incentives to conserve water, provided users can be charged based on how much they use. However, measuring and billing are often technically difficult and costly. There may also be public opposition to charging for water. Water markets can create economic incentives to conserve water, but the infrastructure and institutions to transfer water from one user to another must be in place.
Rationing is a prevalent demand-management measure and can be an equitable way of meeting basic needs because it does not depend on ability to pay, but it may be unpopular and difficult to administer. Rotational irrigation deliveries, limited hours of domestic water supply, or limits on water volumes for industry are examples of rationing.
Other forms of regulation can help reduce demand. Mandating water-saving toilets, flow regulators in plumbing, efficiency requirements for particular industries, and technological measures such as stopping leaks in municipal water supply systems or shifting to sprinkler or drip irrigation can also save water.
Education, social marketing, and public awareness campaigns to change behavior deserve much greater attention in water demand management. Awareness of water problems can motivate water conservation, while education can lead to effective changes in water-use practices. Such campaigns can also make pricing, rationing, or regulatory measures more acceptable to the public and more effective. Finally, measures to reduce water pollution such as regulations on industrial effluents, reductions in agrochemical use, or sewage treatment plants also alleviate water scarcity.
New technologies can increase supplies through low-cost desalination, wastewater treatment, water-lifting devices, or even long-distance transport. Technologies can also reduce water demand and increase productivity through water-saving industrial processes, household plumbing, irrigation devices, or new crops and varieties.
However, past experience has shown that science alone will not solve water problems. Much technology already exists but is not used because organizations and water users do not have the finances, knowledge, or incentives to use them. The right institutions are also required. Instead of separate government agencies for irrigation, water supply, sanitation, and environment, effective water management organizations will have to include new combinations of public sector, private sector, and civil society.
Basin management organizations can coordinate uses and allocate water among different sectors and regions. Effective basin management can result in more efficient and equitable water use and reduce conflict over water, especially in water basins that cross two or more countries.
Allocating water, whether through basin organizations or water markets, requires attention to many types of water rights. Rather than the government trying to establish rigid water rights, it should provide forums for negotiation between different users and claimants and work to strengthen the rights of the poor and disadvantaged groups.
Governments alone cannot and should not be expected to provide sufficient quantities of clean water for all uses. Users' participation in management is crucial for irrigation as well as domestic water supply systems and can contribute to more effective river basin organizations. Creating proper incentives and effective organizations for all users-women and men, poor and rich, from different sectors-to participate is complex and can be costly and time-consuming, but the returns in terms of improved water management, reduced conflict, and long-run sustainability of systems make this a vital investment.
Rapid increases in water use and degradation of water quality are putting extreme pressures on this vital resource. There are a number of strategies for dealing with these challenges outlined in the following briefs, but there is no single solution to overcoming water scarcity and quality constraints. Concerted efforts are needed to increase supplies as well as balance the demands of agriculture, domestic use, industry, and the environment through economic measures, regulation, and campaigns to motivate and equip users to conserve. Technological and institutional approaches must combine to accomplish these goals. Achieving such a coordinated approach to water is challenging, but essential for feeding the world, reducing poverty, and protecting the earth.
For further information see Cosgrove, W. J. and F. Rijsberman. World Water Vision: Making Water Everybody's Business. London: Earthscan Publications Ltd., 2000.
Ruth S. Meinzen-Dick (r.meinzen-dick@cgiar.org) and Mark W. Rosegrant (m.rosegrant@cgiar.org) are senior research fellows in IFPRI’s Environment and Production Technology Division.