Facing a future of water scarcity.

• Author: Postel, Sandra

Enormous savings of the precious liquid are being thwarted by policies and laws that encourage wastefulness and misuse, rather than efficiency and conservation.

Benjamin Franklin once pointed Bout that, "When the well's dry, we know the worth of water." Much of the world is in danger of learning Franklin's lesson the hard way. For decades, water has been wasted, mismanaged, and overused - and the consequences are beginning to hit home.

Water scarcity typically conjures up visions of drought, the temporary dry spells that nature inflicts from time to time. Yet, while droughts capture headlines, the far greater threat posed by escalating water consumption goes largely unnoticed. Despite 1993's floods, water tables are falling, lakes are shrinking, and wetlands are disappearing. Around water-short cities, competition is brewing between city-dwellers and farmers who lay claim to the same limited supply.

In each major area of water use - agriculture, industry, and cities - demands have increased rapidly. Global water use has more than tripled since 1950, and what is removed from rivers, lakes, and groundwater amounts to 30% of the world's stable renewable supply. People actually rely on a far larger share since water bodies dilute pollution, generate electricity, and support fisheries and wildlife. Because of improved living standards, demand has been growing faster than population - per capita use is nearly 50% higher than it was in 1950 and continues to climb in most of the world.

For decades, planners have met this rising demand by turning to ever more and larger water development projects, particularly to dams and river diversions. Engineers have built more than 36,000 large dams around the globe to control floods and provide hydroelectric power, irrigation, industrial supplies, and drinking water to an expanding population and economy. Rare is the river that now runs freely toward the sea, and many that still do are slated to come under control soon.

Limits to this ever-expanding supply are swiftly coming to light, however. Engineers naturally first selected the easiest and least-costly sites for water development. Over time, water projects have become increasingly complex, expensive to build, and more damaging to the environment. Fewer dams and diversion projects are making it off the drawing boards, and most that do will deliver water at a far higher price than in the past.

Meeting human needs while facing up to water's limits - economic, ecological, and political - entails developing an entirely new relationship to the precious liquid. Historically, it has been managed with a frontier philosophy, manipulating natural systems to whatever degree engineering know-how would permit. Modern society has come to view water as a resource that is there for the taking, rather than a life-support system that underpins the natural world humans depend on. Instead of continuously reaching out for more, people must begin to look within their regions, communities, homes, and themselves for ways to meet their needs while respecting water's life-sustaining functions.

Although water is a renewable resource, it also is a finite one. The water cycle makes available only so much each year in a given location. That means supplies per person, a first-order indicator of water security, drop as population grows. Thus, per capita water supplies worldwide are one-third lower than in 1970, due to the 1,800,000,000 people added to the planet since then.

One of the clearest signs of scarcity is the increasing number of countries in which population has surpassed the level that can be sustained comfortably with the water available. As a rule of thumb, hydrologists designate water-stressed countries as those with annual supplies of about 725-1,450 gallons per person a day. When the figure drops below 725 gallons, nations are considered water-scarce - its lack becomes a severe constraint on food production, economic development, and protection of natural systems. Today, 26 countries- collectively home to 232,000,000 people - fall into the water-scarce category. As many of them have very high population growth rates, their problems are deepening fast. Africa has the largest number of water-scarce countries, 11; by 2010, six others will join the list. At that time, the total number of Africans living in water-scarce nations will climb to 400,000,000, approximately 37% of the continent's projected population.

Nine of the 14 countries in the Middle East face water-short conditions, making this the most concentrated region of scarcity in the world. With populations in several of them projected to double within 25 years, a rapid tightening of supplies is inevitable. Since virtually all Middle East rivers are shared by several nations, tensions over water rights are a potent political force throughout the region and could ignite before the end of the century.

Although the population-water equation suggests where to expect trouble, numerous physical symptoms of stress already exist - not just in water-scarce areas, but in parts of water-wealthy ones as well. Among the most pervasive problems is that of declining water tables, which results when groundwater is used faster than nature replenishes it. If pumping is not brought into balance with recharging, the underground supply eventually becomes too expensive to keep tapping, too salty to use as it is pulled up from greater depths, or simply too depleted to serve as a supply. Overuse of groundwater is now ubiquitous in parts of China, India, Mexico, Thailand, the western US., North Africa, and the Middle East.

Some of the most troubling cases of unsustainable groundwater use involve "fossil" aquifers, underground reservoirs that hold water hundreds or thousands of years old and receive little replenishment from rainfall. Like oil reserves, these aquifers essentially are nonrenewable - pumping water from them depletes the supply in the same way that extractions from an oil well do. Farms and cities that depend on this water eventually will face the dilemma of what to do when the well runs dry.

Shrinking groundwater reserves...