Water is rapidly becoming a precious commodity. According to the United Nations, four out of every ten people on the globe now live in areas where water is scarce. By 2025, the U.N. predicts, as much as two-thirds of the world population -- about 5.5 billion people -- may be living in countries facing serious water shortages.

Water -- the lack of it and the misuse of it -- also is at the heart of widespread degradation of the planet's dry lands, a process known as desertification. When water is scarce, thirsty land -- already stressed by overcultivation, overgrazing, and deforestation -- loses its ability to support vegetation, leaving precious topsoil exposed to erosion. The newly barren land cannot absorb water that is available. Rapid runoff leads to further erosion, downstream flooding, silting of rivers, streams, and reservoirs, and reduced water quality in major waterways and ultimately the oceans.

Even beneficial uses of water, such as irrigation of crops, can lead to desertification. Inefficient irrigation practices waste water and contribute to shortages, while over-irrigation robs soil of its fertility through water-logging and especially through build-up of salts left when water evaporates.

To galvanize action on the critical water problems the world faces, the United Nations General Assembly declared 2003 the International Year of Freshwater and 2005-2015 the International Decade on Water for Life. In recognition of the central role of water in the fight against desertification, the U.N also proclaimed water resource management the theme of the ninth World Day to Combat Desertification, celebrated June 17, 2003.

Beyond official proclamations, scientists, officials, and ordinary citizens around the world are working toward better management of watersheds and are exploring a wide range of techniques -- from centuries-old traditional methods to modern high-tech approaches -- to conserve and more efficiently use one of the planet's most precious natural resources.

The Growing Water Crisis

Only about 2.5 percent of the water that covers the earth is fresh water, and much of that is locked in the polar ice caps or deep underground. According to the U.N. Environment Program, less than one percent of the world's surface or below-ground freshwater is available for human use.

Competition for this tiny and finite amount of fresh water is fierce. Water use has soared six-fold during the last century, more than twice the rate of human population growth. One in six people worldwide has no regular access to safe drinking water; half the world's hospital beds are occupied by people suffering from water-borne diseases. Some 200 scientists in 50 countries have ranked water shortages as the most worrying environmental problem for the new millennium.

Water scarcity is the "sleeping tiger" of environmental problems, says Sandra Postel, author of several books on water issues and director of the Global Water Policy Project. "It's going to have very important implications for agricultural production, the quality of the environment, and social and political stability at the local and regional level." Postel has estimated that "additional water supplies equal to 20 Nile rivers could be needed over the next 30 years just to satisfy new food requirements for a still-growing global population."

The Irrigation Dilemma

The problem, in short, is that we are using water faster than nature can replenish it, and much of that use is a result of waste and mismanagement. By far, the greatest waste occurs during irrigation of cropland. About 70 percent of all fresh water is used for agriculture, but an estimated 60 percent of that is lost to evaporation or leakage from inefficient distribution systems. While some water finds its way back into rivers or underground aquifers and may benefit users elsewhere, much irrigation water never reaches the crops it was intended to nourish.

Diversion of water for irrigation is lowering groundwater tables and draining rivers in nations such as the United States, China, and India. The Colorado River in the western United States and the Yellow River in China, for example, often run dry before they reach the sea. Some major lakes, notably Lake Chad in central Africa and the Aral Sea in central Asia, also are dwindling. Irrigation demands and repeated droughts have shrunk Lake Chad to a mere one-twentieth of its size in the mid-1960s, and U.S. scientists predict that the lake is destined to become little more than a "puddle." In the past few decades, the surface area of the Aral Sea has decreased by 50 percent and its volume by 75 percent. The sea's demise is a direct result of the former Soviet Union's diversion of water from the Amu-Darya and the Syr-Darya Rivers, which fed the sea, to irrigate millions of acres of cotton in the deserts of Uzbekistan. What was once the fourth largest inland sea is now mostly degraded land.

But perhaps the greatest tragedy of the Aral Sea -- and the greatest threat from over-irrigation -- is the inevitable build-up of salts left as water evaporates and retreats. The salt concentration of the remaining lake has increased from 10 percent to more than 23 percent, ruining a once-thriving fishing industry, and salt blankets the exposed lake-bed like snow. Winds blow the salt particles and pesticide residues as far as the Himalayas, causing widespread health problems among people in the region and diminishing crop yields, even in fields irrigated with water diverted from the lake.

Salinization is a major contributor to desertification because, as the salt saps soil of its fertility, the land rapidly becomes degraded to the point where it is unable to support any vegetation. In fact, historians believe that salinization of irrigated land may have contributed to the downfall of once-powerful ancient civilizations, such as Babylon and Mesopotamia. Today, an estimated 20 percent of irrigated land suffers from some degree of salinization. As a result, some of the world's most populous nations, such as China, India, and Egypt, are losing significant amounts of arable land.

The economic and social implications of such losses are considerable. Aaron Salzberg, senior advisor on water in the U.S. Department of State, cites the case of Uzbekistan, where 90 percent of cropland is irrigated and 60 percent of that irrigated land is now heavily damaged by salinization. "It is estimated that irrigated agriculture accounts for 35 percent of the country's GDP [gross domestic product], 60 percent of its foreign exchange earnings, and 45 percent of its employment," he says. "So, degradation of the land is going to have a significant impact not only on the country's capacity to grow economically but also on a large portion of the population that is now without jobs."

One promising solution to the irrigation dilemma is drip irrigation, in which water is delivered through perforated tubing on the surface or just under the soil and deposited drop by drop directly to the roots of plants. The method solves the problems of leakage from irrigation channels or canals and evaporation from spray irrigation. Because it is so efficient, it drastically reduces the amount of water needed for crops and slows the build-up of salt in the soil. Pioneered on a wide scale in the 1970s, drip irrigation has enabled farmers to raise crop yields significantly while cutting average water use by a third on each irrigated hectare. Nevertheless, the drip method is still used on less than one percent of the world's irrigated land.

A nonprofit organization in India, International Development Enterprises, is trying to change that statistic by promoting simple, affordable drip systems to small farmers, who account for about 78 percent of India's growers. The cheapest, simplest kit consists of a bucket and a filter made from a plastic bottle, which can be used to irrigate 100 plants over a 25 square meter plot. A larger "drum kit" version can irrigate 100 square meters.

A much more high-tech solution to the salinization problem is the genetic engineering of salt-resistant plants, known as halophytes. a process well-developed in Israel. In Pakistan, where desertification caused by salinity is a major problem, researchers are exploring use of halophytes as sand-binding plants, for cattle forage, and to produce seeds that yield cooking oil.

Solutions Large and Small

While irrigation innovations are important, they are only one part of the solution. There is the ever-present challenge of ensuring an adequate supply of water to meet all needs. As global water use has skyrocketed, "engineers have met rising demands by building larger water projects and drilling ever more groundwater wells," says Postel. "But limits to expanding the supply are swiftly coming to light." The mega-projects are coming under increasing scrutiny and criticism because of what some see as their exorbitant costs, environmental destruction, and displacement of indigenous people.

There still is a need for dams and other water storage systems in parched countries, notes Aaron Salzberg. "In the United States, we have more than 6,000 cubic meters of water storage per capita, but in Ethiopia that number is 100 times less. We can survive a drought without famine, Ethiopia can't."

But more and more, water experts are looking to conservation and efficiency to solve water woes. Research has shown that in most cases people are more likely to use water sustainably if they have a say in management of water supplies. On the local level, variations on simple, traditional approaches for capturing and storing water are proving valuable for ensuring a stable supply. In the highlands of Yemen, for example, the International Center for Agricultural Research in Dry Areas and Canada's International Development Research Centre helped farmers find ways to rebuild and buttress ancient water-saving terraces that had fallen into disrepair. As a result, men who had left the area to seek jobs in the cities eagerly returned to farming, discovering that food production in the newly-fertile fields was a profitable occupation.

On India's Deccan Plateau, Canadian and Indian researchers helped 10,000 poor tribal families use their own knowledge of the land and water sources to plug gullies and create small diversion systems to slow runoff and reduce erosion during the rainy season. Water pooled and seeped into the soil, increasing crop yields and replenishing groundwater supplies. The people also were encouraged to build rooftop rain collectors and storage tanks to provide year-round water supplies so that women and children would not have to spend every day of the dry season finding and carrying water to their families.

Indeed, rooftop rain harvesting has been practiced for centuries in chronically dry areas and in monsoon climates with seasonal downpours. The main challenges are keeping the water clean and developing cost-effective storage systems that can serve entire communities. An organization in New Delhi, the Center for Science and Environment, is actively promoting rainwater harvesting throughout India via training sessions, publications, videos, and its Web site. The organization provides detailed guidance for both urban and rural communities, using a variety of traditional and modern collection and storage devices.

Newer technology to capture water from the fog that forms along coastal cliffs or the dew from night winds has shown promise in arid regions around the world, from Chile and Peru to Oman, Nepal, and Tanzania. But so far these methods have not proved practical or economical on a large scale.

As water has become more precious, people in communities of all sizes are turning to creative ways of reusing wastewater. In small, impoverished communities in Senegal and Peru, aquatic plants such as water lettuce are successfully converting household wastewater to irrigation water safe for small vegetable gardens. Large-scale systems, such as an engineered wetland designed to treat all of the wastewater in Battambang, Cambodia's second largest city, have not proven as cost-effective.

Another relatively new area of water research and management involves recharging of aquifers -- underground waters flowing through bedrock and deep soil -- that have been depleted by overpumping or degraded by salinization and chemical contaminants. Recharging techniques also range from the simple, such as digging pits or trenches to collect rainwater, to the high-tech, such as injecting clean water under pressure into fissures in bedrock.

There is no one solution to water problems that works in every situation, notes Salzberg. Conservation techniques "must be adapted to a particular community, must be sustainable, and people have to commit to them," he says. "The challenge to us is to create a large enough toolbox, so to speak, so that people can pull from it the tools that are appropriate for them in their technical, social, and cultural setting."

Watershed Management

Reducing waste and assuring equitable distribution of water on a large scale requires responsible management of entire watersheds. By definition, a watershed is an area of land from which water drains on the surface or as groundwater into a common lake, stream, or river. Everyone on earth lives in a watershed, and everywhere land use upstream affects water quality for all those who live downstream.

One issue is that watersheds follow the topography of the land; they do not respect political boundaries. "It's ironic that we often use rivers to delineate political boundaries, when in fact they may well run through a watershed that spans two countries," says Sandra Postel. "On the one hand, that river marks a boundary, but on the other hand it represents an ecological connection." About 40 percent of the world's population now lives in river basins shared by more than one nation.

Watershed management, then, may require an exceedingly high level of cooperation at all levels -- among villages, municipalities, states or provinces, nations, and entire regions. Although political unrest in some areas, especially the Middle East, has stymied efforts to produce regional water treaties, other parts of the world have made strides toward defusing water-related tensions. India and Bangladesh have signed a treaty on sharing the dry-season flow of the Ganges River, and the Nile basin countries meet regularly to foster cooperation on allocation of the river's water.

A New Water Ethic

Ultimately, it will require what Sandra Postel calls "a new water ethic" on the part of individuals, communities, and governments if we are to solve the water crisis and combat desertification. "Water is not just a commodity like oil or copper; it's the fundamental basis of life on earth," Postel notes. "We have to realize that water is finite, and it needs to be used and shared more equitably not just among people and among countries but also between ourselves and nature."