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Population and the Future of Renewable Water Supplies


Population and the Future of Renewable Water Supplies: The first update in the SSI Population-Environment Linkages Series focuses on the relationship between population growth and fresh water availability. Water availability has not received the attention it deserves in global discussions of the sustainable use of natural resources, and it has been examined even less in the context of population growth. Through a series of case studies, this update explores the causes and consequences of water scarcity and explains the importance of slower population growth-and eventual population stability-in helping to achieve sustainable global water use


An information update produced jointly by the Union of Concerned Scientists and Population Action International

October 1998

[This update cannot be reprinted or reposted to electronic networks without permission and acknowledgement.]

Of all the planet's renewable resources, fresh water may be the most unforgiving. Difficult to purify, expensive to transport, and impossible to substitute, water is essential to food production, to economic development, and to life itself. There are currently more than 430 million people living in countries considered "water stressed." Population Action International (PAI) projects that by 2050, the percentage of the world's population living in water stressed countries will increase by at least threefold.

Before examining in detail some specific examples of regional water stress, it is useful to review the criteria for quantifying the relationship between population growth and water availability. Swedish hydrologist Malin Falkenmark originated the idea of a "water stress index" based on an approximate minimum level of water needed per capita to maintain an adequate quality of life in a moderately developed country. Working with existing hydrological principles and benchmarks, Falkenmark estimated that 100 liters (26 gallons) per person per day is the rough minimum required for basic household needs such as drinking, bathing, and cooking. She further determined that five to 20 times this amount is needed to meet the demands of the agricultural, industrial, and energy production sectors (Falkenmark and Widstrand 1992).

Based on these calculations, Falkenmark derived benchmarks indicating the onset of water stress and water scarcity. A country with more than approximately 1,700 cubic meters of renewable fresh water per person per year will generally experience only intermittent or localized water shortages. As the amount of available fresh water sinks below this level, countries begin to experience "water stress"-that is, water supply problems tend to become chronic and widespread. This stress indicator is a caution light, signifying that population growth is reducing the amount of available water per person to troublesome levels. As the renewable water supply falls below 1,000 cubic meters per person, the more serious "water scarcity" begins to occur. For most countries in this category, chronic water shortages can hamper food production and economic development and cause serious environmental degradation (Falkenmark and Widstrand 1992).

Although these widely used indices of water stress and scarcity are extremely helpful to clarify the relationship between water use and human population growth, they cannot by themselves tell the whole story. These indices do not distinguish, for example, whether the fresh water in any given country is available at the time when it is most needed (e.g. for crop irrigation) or in the places where it is most needed (e.g. near population centers). Some experts argue that the global freshwater crisis is actually worse than the stress and scarcity indices suggest. For a more complete picture, these experts recommend that when possible, regional availability, along with physical indicators, be taken into consideration when evaluating the conditions of water availability for any locality. Throughout this update, the water stress and scarcity benchmarks are used to illustrate concepts of water availability on a national scale.



Applying these benchmarks to the data for renewable water by nation, currently 166 million people in 18 countries are suffering from water scarcity, while almost 270 million more in 11 additional countries are considered water stressed (World Resources Institute 1996). PAI estimates that by the year 2050, according to the UN 1996 medium projection, the percentage of the world's population in countries experiencing water stress and scarcity will increase more than fivefold-from eight percent in 1995 to 42 percent in 2050.

This demographic pressure has led one international water resources expert to predict that for these and many other countries, the lack of adequate supplies of renewable fresh water could soon become the main constraint on their economic development (Biswas 1992). This is already the case in several water scarce countries in northern and southern Africa, where population growth rates remain high and increased pressure is placed on limited water resources to meet the growing demand for food production. In fact, all of the five countries projected to cross the water scarcity benchmark within the next 10 years are in Africa-adding more than 100 million people to those already coping with severe water resource shortages.

In these and many other countries, increasing water scarcity will increase the cost of producing and delivering fresh water just to keep pace with current levels of service. This increased cost will drain financial resources that would otherwise be available for investment in the development of other sectors of the economy (Khroda 1996). With the United Nations projecting that more than 90 percent of population growth between now and 2050 will occur in developing countries (United Nations Population Division 1996b), the demand placed on freshwater resources by these countries will make sustainable economic development increasingly difficult. The following three examples of regional water stress provide some indication of the seriousness and extent of the threats to the future of renewable water supplies.


A situation with serious international implications is the growing demand for the waters of the Euphrates River by Turkey, Syria, and Iraq. Originating in Turkey and flowing south through Syria and Iraq into the Persian Gulf, the mEuphrates is the primary water source for millions of people mwho depend on it for power generation and irrigation in an mextremely arid climate. Although the conflict over water mbetween these countries is decades old, it has intensified min recent years as a result of a massive Turkish dam mbuilding program known as the Greater Anatolia Projectm (GAP). Designed to provide a supply of water and power madequate to fuel the development needs of Turkey's population-which is growing at l.6 percent annually-GAP is mone of the most massive water infrastructure projects in mhistory. When completed, it will provide Turkey with a generating capacity of 7,500 megawatts of electricity-nearly four times the capacity of Hoover Dam-and open at least 1.5 million hectares of land to irrigated cultivation (Kolars and Mitchell 1991).

Though GAP promises to bring prosperity to the estimated seven million Turks who live in the region, Syria and Iraq have good reason to worry about the project's impact on their water supplies. Full implementation of the GAP system of dams could result in a 40 percent reduction of the Euphrates' flow into Syria and an 80 percent reduction of flow into Iraq. Such a scenario has the potential to reduce the electrical output of one of Syria's primary power sources to 12 percent of capacity, while Iraq could lose irrigation water to approximately 20 percent of its total arable land. Reduction of the river's flow, combined with Turkish development fueled by the project, will increase theEuphrates' salinity level as well as increase agricultural and industrial pollution in the remaining waters left to flow into Syria and Iraq (Jansen 1990).

Both Syria and Iraq have already threatened war over their access to the Euphrates, heightening the urgency of a regional water-sharing agreement before the existing water shortages become even more acute (Wolf 1996). As the populations of these nations continue to expand-driven by fertility rates well above the global average-the competition for fresh water between agriculture and development could give rise to increased instability in a region that is already dangerously unstable.


Perhaps the most vivid example of the interaction of population growth and water scarcity is the vast basin of the Nile River in northeastern Africa. The 10 countries with territory in the Nile basin contain 40 percent of Africa's population (not all actually within the basin) and make up 10 percent of its land mass. More than 85 percent of the Nile's water comes from the Blue Nile, which originates in Ethiopia (Postel 1992). The vast majority of the river's flow, however, is used by Egypt, the last nation on the Nile's path to the Mediterranean Sea (Wolf 1996).

For centuries the cultural symbol of Egypt, the Nile provides almost all the fresh water used by more than 60 million Egyptians living along its banks. When few people lived upstream-and modern economic development was a distant dream for the entire basin-Egypt saw no reason to worry about its dependence on the Nile's waters. Its complacency is now ending, however, as the upstream nations begin to harness the Nile's waters to provide economic prosperity for their own growing numbers.

Ethiopia, for example, recently emerged from a long period of civil war and famine into a period of accelerated growth and economic development. The government has overseen the construction of more than 200 small dams that will use nearly 500 million cubic meters of the Nile's flow annually. Additional dams are planned to increase the country's irrigation and hydropower capacity (Marcus 1997). Though Ethiopia's current development plans will require only a small portion of the Nile's water, its potential demands could significantly reduce the river's flow into Egypt. Ethiopia has an estimated 3.7 million hectares of land-an area larger than Belgium-that could be irrigated (Postel 1996). With a population nearly the size of Egypt's and a faster annual rate of population growth-3.2 percent annually for Ethiopia versus two percent for Egypt-Ethiopia will need to develop a large portion of this land for agricultural use (United Nations Population Division 1996a). Irrigating only half this land area with water from the Nile could reduce the river's flow to Egypt by 15 percent (Postel 1996).

Egypt itself is raising the stakes with ambitious plans for its New Valley land reclamation project. Pressed by population growth within its own borders, the Egyptian government has begun a massive irrigation project in the country's western desert in an attempt to persuade seven million Egyptians to move there from the crowded Nile Valley. When completed, a pipeline will carry up to five billion cubic meters of Nile water from the Lake Nasser reservoir to the New Valley site to facilitate the construction of new cities and provide irrigation to more than 200,000 hectares of desert-an area more than twice the size of New York City. Hydrologists doubt the basin produces enough renewable fresh water to satisfy the irrigation plans of both Ethiopia and Egypt (Marcus 1997).

Sudan, meanwhile, plans to build its own dam on the Nile north of the capital, Karthoum, where the Blue Nile and the White Nile converge before flowing into Egypt (Marcus 1997). The remaining Nile basin countries currently use only a small portion of the river's water. With their cumulative population now numbering over 140 million, however, and projected to grow to more than 340 million by the year 2025, it is inevitable that these countries will soon begin to lay claim to a larger share of the Nile's flow to meet their growing irrigation and development needs (United Nations Population Division 1996a). In recent years, representatives of the ten nations of the Nile watershed have met to review past agreements and consider possible future ones related to their use of this shared natural resource (Guddaa 1997).

The whole world is watching the Nile and similar international watersheds. At a March 1997 forum on international water issues in Marrakech, Morocco, UN Secretary General Kofi Annan stressed that the projected growth of world population over the next 30 years makes developing cooperative international agreements on shared water resources "one of the most urgent issues on the global agenda" (United Nations 1997a). Later that year, the UN General Assembly approved a convention to establish guidelines for cooperation on sharing the benefits of international watercourses (United Nations 1997b). The US State Department and Environmental Protection Agency have opened field offices called environmental hubs to help developing nations negotiate transboundary solutions to regional environmental problems such as freshwater scarcity, deforestation, and air pollution, and to raise the profile of environmental issues in global diplomacy. The Eastern Africa hub, which specializes in Nile Basin water resource issues, recently opened in Addis Ababa (Marcus 1997).


As stated earlier, national-level water stress benchmarksare not always sufficient in illustrating the seriousness of water shortages over time or within a given region of a nation. One example of such a mismatch between available water and the greatest need is in the southern region of Africa, where Namibia and neighboring Botswana are engaged in a dispute over use of the Okavango River. On the basis of the amount available per person, Namibia seems to have a relatively abundant freshwater supply. Namibia, however, has no perennial rivers, only seasonally flowing ones that are reduced to a trickle several months of the year. Further, Namibia is the driest country in sub-Saharan Africa-nearly 83 percent of all rain evaporates soon after it falls, and only one percent of what remains is available to recharge groundwater aquifers (Eales, Forster, and Du Mhango 1996).

Traditionally, this was not a problem in many regions of Namibia, where the mostly rural population would simply move to other water sources during the dry season. Rapid population growth and more densely populated human settlements, however, are hampering this migratory lifestyle. To meet the needs of its growing population, Namibia has in recent years been forced to experiment with a variety of water supply options, including desalination and pumping groundwater from its fossil aquifers. The cost of large-scale desalination has thus far proved prohibitive, as Namibia's major population centers are too far inland for water to be pumped economically from the coast. The desalination plants that do operate require enormous amounts of energy, generating levels of pollution that are excessive relative to the volume of fresh water produced. Additionally, the over-pumping of groundwater has already led to dangerous increases in salinity as well as the rapid depletion of the aquifers themselves (Eales, Forster, and Du Mhango 1996).

This has led Namibia to launch a planning process aimed at extending its already massive network of supply pipelines to the Okavango River, which runs throughout the year along its northeastern border with Angola. The plan would divert an estimated 20 million cubic meters of water from the river through the 155-mile pipeline. The problem is that the river flows into Botswana, where it feeds the largest delta-and one of the most delicate aquatic ecosystems-in the world (Matloff 1997). The Okavango River situation is illustrative of other aquatic ecosystems around the world, where large-scale diversions of fresh water from natural ecosystems for hydroelectric power, drinking water, or irrigation deplete fisheries, increase salinity pollution levels, and lead to a loss of biodiversity in and around the rivers, wetlands, and lakes from which water is taken.

With its water needs expected to double within the next 20 years (Eales, Forster, and Du Mhango 1996), Namibia sees the pipeline as the only feasible solution to keep pace with the water demands of its growing urban centers. Botswana, on theother hand, contends that the diversion could damage thebiologically diverse marshlands along the Okavango Delta-which is Botswana's main tourist attraction-and dry up the floodplain along which most of the delta's 100,000 inhabitants live (The Economist 1997). Hydrologists now predict that Windhoek, Namibia's capital, could begin to runshort of water in 1998 (Eales, Forster, and Du Mhango 1996). The need for both governments to negotiate a long-term solution is clearly urgent.



While the above case studies focus on the problem of water scarcity itself as a major natural resource issue, stresses on renewable water supplies compound other environmental problems. Although fresh water represents only a fraction of the Earth's water, it supports an exceptional number of animal species. Most freshwater ecosystems are feeling the impacts of increased human intervention in natural systems.

Dams block the return of salmon to spawning areas, for example, and toxic pollution and acid precipitation kill fish. Fertilizers leaching into freshwater supplies promote the growth of algal blooms in surface waters. In China, for example, the growth of algae stemming from human, agricultural, and industrial wastes has reduced oxygen levels in rivers to the point that only five of fifteen river stretches sampled recently near large cities could support fish (World Bank 1992). Toxic metals contribute to waterfowl deformities, and industrial heavy metals expelled into water accumulate in fish and shellfish, concentrating in those higher up in the food chain.

On the most extreme end of the water scarcity continuum, whole freshwater ecosystems are disappearing as rivers and coastlands are developed around the world. The United States' Florida Bay, for example, has undergone dramatic changes since a rapid influx of people into South Florida began in the 1940s. The bay-most of which lies within the boundaries of Everglades National Park-has been transformed from a healthy estuary to a nearly lifeless, hyper-saline lagoon (Lear 1993).

Looming over questions of future water supply and use is the likelihood that human beings are changing climate worldwide through the heat-trapping greenhouse gases their activitiesincreasingly release into the air. The impact of the predicted global warming on renewable water supplies and demand is not yet known with certainty, but global warming is likely to change rainfall, storm patterns, and sea levels. Preliminary studies have suggested as much as a 25 percent decrease in the runoff of the Nile and similarlosses in the rivers of the southwestern United States (Clarke 1993, Gleick 1992). Moreover, some climatologists predict global warming will intensify the extremes of the water cycle, exacerbating drought and bringing more rainfall in deluges that ultimately is lost in floods. The midwestern United States' swing from searing drought in 1988 to record-breaking flooding five years later illustrates how damaging climate extremes can be. The risk of substantial changes in climate over the coming decades, coupled with the otherthreats posed by growing human pressures, underlines the uncertainty about our future water supply.



The 1996 United Nations population projections show that world population growth is slowing more dramatically than previously thought. As a result, the world could have 450 million fewer people in the year 2050 than the United Nations projected just four years ago. (The medium variant projection in 1994 was 9.8 billion; this number was reduced to 9.4 in the 1996 revisions.) This reduction is primarily the result of significant declines in birthrates throughout the world. (For further information on population decline, please see the 3/19/98 SSI Info Update "What Birth Dearth?") While this is in and of itself good news, reductions in population growth also have beneficial effects on the amount of renewable natural resources such as water, air, and forests that are available to each person on the planet.

The new UN projections suggest that the future of water availability looks slightly brighter, largely as a result of lower rates of population growth in many countries around the world. Under the UN's medium variant scenario, PAI's new projection shows almost 400 million fewer people living in water stressed or scarce countries in 2050 than was predicted in 1994.

The impact of reduced population growth on water resources becomes even more apparent at the country level. When applying the national level benchmarks, PAI now estimatesthat the transition into a condition of water stress by such countries as Sri Lanka and El Salvador will be delayed by at least 10 years as a result of the slower population growth rates reflected in the 1996 UN projections. In countrieswith already sizable populations, the effects of slower population growth on water resources can be even more dramatic. India, for example, whose current population approaches one billion, was projected in 1994 to begin experiencing water stress as early as 2015 and to remainwater stressed through at least the year 2050. Under the new UN projections, however, it is conceivable that India will not cross the water stress benchmark until 2035, a decade later than the most optimistic projection made in 1994.

Postponing such transitions can provide much needed breathing room during which countries facing water shortages can take steps to develop their existing water resources, improve the efficiency of water usage patterns, and implement water conservation programs.

Do these new data mean water availability is improving? Hardly. Even given the more encouraging population projections from the 1996 UN data, the problem of water scarcity will still get worse before it gets better. But what this comparison shows is that even small changes in the

population growth rate can have enormous implications for future generations. This improved assessment of the future availability of renewable fresh water has a wide range of potential benefits, from less pressure on freshwater ecosystems and underground aquifers to less tension between nations competing for shared water resources. Even under this improved scenario, however, renewable freshwater scarcity will continue to remain a problem for millions of people around the world; the good news is that slowing population growth can reduce the severity and duration of such natural resource scarcities. 

Population growth rates do not, however, slow down on their own. They result from the desires of hundreds of millions of women and men to have fewer children-and the efforts of governments and other institutions to help them achieve these goals throughout their reproductive years. Now more than ever, sound policies that will promote the transition to a stable population size-including improving access to family planning, expanding educational opportunities for girls, and providing economic opportunities for women-remain critical. Pursued consistently, such efforts can delay the onset of water stress and scarcity in many countries, buying precious time for strategies that can make freshwaterresources endure for generations to come. 



-- Efforts to slow population growth today can reduce the severity and duration of fresh water scarcity tomorrow. Over the next few decades, continued population growth will almost certainly exacerbate the already severe water scarcity facing many countries.

-- An adequate and dependable supply of fresh water is essential for human health, food production, and economic development.

-- Today there are nearly half a billion people-eight percent of the world's population-living in 29 countries affected by water stress or the more serious condition of water scarcity.

-- Water scarcity will continue to worsen for several decades. How fast the world's population grows between now and the middle of the next century will determine whether the number of people affected by water problems grows to two billion or to as high as seven billion.

-- Slower population growth delays the onset of fresh water scarcity. As a country's population increases, so, too, does the demand for fresh water for food production, industry, and domestic use. Slower population growth brakes the acceleration in demand for fresh water, effectively buying time for countries to adapt to these new constraints. This additional time will provide much-needed breathing room to develop alternate sources of water, to switch to more efficient irrigation techniques, and to implement water conservation plans.

-- Policies that have been shown to reduce birthrates-such as improving access to family planning, expanding educational opportunities for girls, and providing economic opportunities for women-can also reduce the problems of freshwater scarcity and help ensure that our limited fresh water resources can sustain us for generations to come.

-- Slower population growth reduces the risk of conflict over scarce water resources. This is especially true in such regions as the Middle East and North Africa that face a triple threat of rapid population growth, an arid climate, and shared water resources.

-- Slower population growth protects aquatic ecosystems. Large-scale diversions of fresh water from natural ecosystems for hydroelectric power, drinking water, or irrigation deplete fisheries, increase salinity pollution levels, and lead to a loss of biodiversity in and around the rivers, wetlands, and lakes from which water is taken.

[This information update is based on the following reports by Population Action International: "Sustaining Water: Population and the Future of Renewable Water Supplies" (1993) and "Sustaining Water, Easing Scarcity: A Second Update" (1997). To order the full text of these reports, please visit the Population Action International website at or contact Tom Gardner-

Outlaw at Katie Mogelgaard summarized and reformatted the information. Fred Meyerson, Sandra Postel, and Nancy Cole provided review and comments.] 


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Postel, Sandra. (1992) Last Oasis: Facing Water Scarcity. W.W. Norton, Worldwatch Institute: New York. 

Postel, Sandra. (1996) Dividing the Waters: Food Security Ecosystem Health and the New Politics of Scarcity. Worldwatch Institute: Washington, DC.

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United Nations Population Division. (December 1996b) "World Population Prospects. The 1996 Revision." Population Newsletter, no. 62.

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