RAND Review
One World, One Well
How Populations Can Grow on a Finite Water Supply
By Jill Boberg
Jill Boberg is an environmental policy analyst and a RAND consultant.
Earth is called the water planet, as water covers 71 percent of the Earth’s surface, with additional water lying in glaciers, icecaps, the atmosphere, and underground aquifers. However, very little of this water is available for human use. Of the 1.4 billion cubic kilometers of water on Earth, only a tiny fraction of it — 200,000 cubic kilometers, or just 0.014 percent — is fresh water accessible for human needs, including water for the ecosystems on which humans depend.
The availability of fresh water has become a pressing global concern because of unprecedented growth in the human population. The demand for naturally recycled fresh water continues to grow while the supply remains all but fixed. The greatest growth in demand is occurring in developing countries, which have the fewest natural, social, and economic resources to meet it.
The proliferation of smaller households may do more environmental damage than does simple population growth. |
To avert a global water crisis, local and national water managers need to understand the effects of demographic factors on water demand and institute reforms to help people safeguard the water supply. Some policy tools can help reduce demand, while others can help augment the supply available for human use. Equally important is revamping the governance of many water systems.
Demand by Sector and Population
Agriculture accounts for nearly 70 percent of all the fresh water used worldwide (see Figure 1). Industry accounts for about 20 percent. Domestic uses account for the remaining 10 percent. But the relative proportions of water withdrawn by each sector differ considerably from continent to continent. The dominance of agriculture tends to decline with higher levels of industrialization.
The world’s changing demographics will have a strong effect on the Earth’s freshwater supply. Population expansion, household contraction, urbanization, and economic development will all increase the amount of water withdrawn and influence the quality of water available.
| Figure 1 — Agriculture Accounts for Nearly 70 Percent of Annual Freshwater Usage Worldwide |
SOURCE: World Meteorological Organization, Comprehensive Assessment of Freshwater Resources of the World, New York: World Meteorological Organization, 1997. |
| Figure 2 — Population Growth Has an Enormous Influence on Water Availability |
SOURCES: Igor A. Shiklomanov, Archive of World Water Resources and World Water Use, Global Water Data Files, State Hydrological Institute, St. Petersburg, Russia, CD-ROM, 1998; Peter H. Gleick, “The Changing Water Paradigm: A Look at Twenty-First Century Water Resources Development,” Water International, Vol. 25, No. 1, 2000, pp. 127-138, available online as of March 2006. |
The tripling of the human population in the past 70 years has been accompanied by a sixfold increase in water withdrawals. Of greater concern, the number of households worldwide has increased at a rate even faster than that of population growth — the result of lower fertility rates, higher divorce rates, aging populations, and a decline in multigenerational family units.
The proliferation of smaller households may do more environmental damage than does simple population growth. Per capita, smaller households consume more water and produce more waste than do larger households. By requiring more housing units, smaller households also consume more construction materials and contribute to urban sprawl. Urban sprawl damages water quality by paving over land that would otherwise help filter the water that replenishes lakes and rivers.
Increasing urbanization is both a symptom and a cause of strained water supplies. When farmers migrate to cities, it is often because of deforestation, desertification, drought, or lack of arable land. Migration to cities inflicts several negative consequences on urban water resources: depleting municipal water supplies, generating more waste than the surrounding environment can absorb, contaminating local groundwater, and ultimately requiring waterborne sanitation systems that alone increase the demand for fresh water by about 40 liters per capita per day.
In terms of economic development, industrialized countries use more water per capita than do developing countries to run industry, grow food, produce electricity, and process waste. People in industrialized countries also demand more water-intensive products and services.
Supply by Region
Much of the world’s water lies far from population centers. A large percentage of the water is found in the Amazon basin, Canada, and Alaska. About three-quarters of annual rainfall comes down in areas where less than one-third of the world’s population lives. And because rainfall and river runoffs occur in very large amounts in very short time periods, many people cannot make use of most of the world’s freshwater supply.
Figure 2 shows both the large variation across continents in the availability of “blue water” (the annually renewable supply of fresh water that can be tapped without leading to its depletion) and the effect of population on availability. The two extreme cases are Asia and Australia/Oceania. Asia has the highest total water availability but the lowest per-capita availability, whereas the opposite holds true for Australia/Oceania because of its lower total population.
Figure 3 gives a clearer picture, showing the per-capita renewable water supply by river basin. Looking again at Australia, it is clear that some areas — the most populated areas — have large per capita supplies of water, whereas other parts of the continent, where very few people live, have very small per-capita supplies of water. In Asia, although the continent as a whole has relatively low per-capita water availability, some areas are quite well endowed with water.
| Figure 3 — Annual Renewable Water Supply Per Person Varies Greatly Across and Within the Continents |
SOURCE: Liquid Assets, 2005. |
Cap Demand First
The tools chosen to manage water will depend on local conditions, but demand management will almost always be critical. Especially important in developing countries, demand management could defer large investments in water supply infrastructures, essentially buying time. In fact, a $2 million investment in demand management could delay a $200 million investment in new infrastructure for ten years, according to the United Nations Centre for Human Settlements.
To cap demand, water managers can choose among the following policy tools: institutional and legal changes, market-based incentives, nonmarket instruments, and direct interventions.
Some types of institutional and legal changes are more controversial than others. One is water-quality matching, which channels pure water only to functions that require it, such as human consumption, and lower-quality water to things like irrigation and industrial processing. Another is decentralization, which allows local communities to control their own water supplies.
The most controversial change of this type is privatization, or involving private firms in building and operating water-management systems. It is controversial because these firms are motivated by private profits, whereas water is usually believed to be a common good. Before privatization becomes a widely available option, concerns must be addressed about equitable access to water for the poor, the integration of environmental priorities, and the sharing of environmental risks.
Among the market-based incentives, the most common is water pricing. Huge public subsidies now flow to agricultural users in most countries. In the United States and Mexico, agricultural users pay only about 11 percent of the full cost of water. Water pricing may raise or lower prices for all or certain users, adjust subsidies and taxes, and levy charges for pollution flows or effluents. Such reforms typically reduce demand, increase conservation, enhance environmental sustainability, and spur reallocation among the agricultural, industrial, and domestic sectors.
Nonmarket instruments consist mostly of laws and regulations — such as quotas, licenses, pollution controls, and usage restrictions — to control water consumption. Educational campaigns to encourage water conservation are important complements to other nonmarket instruments.
Direct interventions include technological and other measures to conserve water. Examples are leak detection and repair programs, efficiency standards for plumbing fixtures, investments in infrastructure, modified industrial processes, and shifts toward water-efficient crops.
As a general rule, one of the best and most cost-efficient ways to secure water supplies around cities is to conserve forests. |
Tap Supply Next
While demand management promotes conservation and efficiency, supply management involves the location, development, and exploitation of new sources of water. Again, local conditions will dictate the best balance among the supply management options described below.
Dams and water-control structures are used for electric power generation, flood control, water storage, irrigation, and domestic water provision, thus offering substantial benefits. However, dams have large environmental, social, and demographic consequences, such as the submergence of forests and wildlife, the release of greenhouse gases from the decay of submerged vegetation, the relocation of families, the destruction of villages and historic and cultural sites, the disruptive effect of altered river routes, and the risk of catastrophic failure. Currently, there are more than 41,000 large dams worldwide. The costs of such projects have reached their financial, legal, and environmental limits in most industrialized and some developing countries.
Small-scale irrigation systems could expand with fewer constraints than could large-scale water projects. But success depends on factors such as technology, infrastructure, and implementation.
Groundwater is an efficient source of irrigation water because it can be tapped when and where it is needed, reducing transportation costs. However, sustainable use of groundwater requires oversight to ensure that the amount tapped does not exceed the amount recharged each year. Because many developing countries depend on groundwater for irrigation, and on irrigation for the food supply, the uncontrolled depletion of groundwater aquifers poses a serious threat to food security in many areas, particularly the northern China plains and western and peninsular India.
Reforestation of degraded and unproductive land can be cost-effective in the long term if all the ensuing benefits are taken into account: better water supply, larger agricultural revenues, and less pollution. But the high initial cost, combined with the drive to find short-term solutions, makes reforestation less appealing in many regions. This is especially true in densely populated poorer countries, where competition for land and resources is fierce. As a general rule, though, one of the best and most cost-efficient ways to secure water supplies around cities is to conserve forests.
Interbasin transfers and water exports are two more ways to bring water to places with dense populations or insufficient supplies. Interbasin transfers (using canals or pipelines to transport water) require infrastructures that are expensive and potentially environmentally harmful, both to the freshwater ecosystem from which the water is extracted and to the lands over which the pipes or canals must flow. Meanwhile, selling water through exports has been controversial because, again, water is perceived as a common resource that should not be sold by private companies.
Water reallocation among the agricultural, industrial, and domestic sectors can be accomplished either via government mandates or via market incentives. Reallocation from agricultural to other uses is already occurring in Chile, California, and elsewhere. Because water in developing countries is consumed predominantly by agriculture, reallocating even small percentages of the water to the domestic sector can fill that sector’s needs.
Desalination, or turning saltwater into fresh drinking water through the extraction of salts, is an extremely expensive, energy-intensive process that produces brine that must be disposed of carefully to avoid environmental damage. For these reasons, desalination is an unappealing option, except in arid, relatively wealthy countries, such as Kuwait, Saudi Arabia, and Israel.
Water harvesting, or the capture and diversion of rain or floodwater, is an agricultural tradition now being adapted for urban domestic purposes. Required in new buildings in some Indian cities, water harvesting can both decrease the polluted runoff in urban areas and increase the efficiency, productivity, and soil fertility in rural areas.
Water reclamation and reuse have cut industrial water use in some developed countries, notably Japan and the United States, while reducing the pollution released by industry into oceans, lakes, and streams. Wastewater and gray water (from showers and sinks, for example) can be used in gardens or stored in soak pits for groundwater recharge. Several such schemes are already in operation in Israel, Portugal, Tunisia, Namibia, California, and Japan and are being considered or pursued in Morocco, Jordan, Egypt, Malta, Cyprus, Greece, Spain, France, and Italy. The practice is limited, though, wherever the water contains high levels of salts or heavy metals.
Pollution control laws in developed countries have helped to clean up rivers, lakes, and streams and to promote conservation and efficiency. Although most countries have pollution-control laws, many developing countries lack the political will or financial resources to enforce them.
A Parched Planet?
There will continue to be localized problems of water scarcity and perhaps widespread problems in some areas. But a global water crisis can be averted. There are numerous ways to improve water management and to satisfy demand, even for growing populations. The best set of tools for any given location will depend on its social, political, economic, and physical climate.
Attention to demographic factors is an important part of the formula for staving off a water crisis. Sustainable water development and management will require the integration of social, economic, and environmental concerns. This effort will be enhanced by research that focuses on as small a scale as possible,
preferably the scale of natural watersheds, to help policy-
makers around the world manage water at levels that are both socially and environmentally relevant. 
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