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Safeguarding Our Water 

Scientific American Feb01

Peter H. Gleick

Editor's Introduction

Drip, trickle, splash. Water is one of the most common substances in the universe, and our ocean-wrapped planet is blessed with a generous share of it. Unfortunately, 97 percent of that share is salty, and much of the rest is locked up in ice. Obtaining an adequate supply of freshwater has consequently been the focus of human ingenuity and passions throughout history. Water has been the prize (and sometimes the weapon) in conflicts around the world. Even in the century ahead, impressive gains in technological capabilities to find, transport and conserve freshwater may not be able to accommodate increasing demand, particularly in the developing world. Local mismatches between need and supply could push groups to violence, retard economic progress and devastate populations.

In the following pages, Peter H. Gleick of the Pacific Institute for Studies in Development, Environment and Security describes the magnitude of the world's pressing water problems in terms of skyrocketing usage and ominous limits to the known supplies. Sandra Postel of the Global Water Policy Project then narrows the discussion to irrigation, the single largest use for freshwater, and to the prospects for improving this vital agricultural technology. Lest anyone think that other options for staving off water shortages are lacking, we also consider a quartet of other approaches, including desalination, "bag and drag" transport, recycling and increased plumbing efficiency. A water crisis may be in the cards for some, but not if we act quickly to develop all the solutions at our disposal. --The Editors

Making Every Drop Count

Peter H. Gleick

We drink it, we generate electricity with it, we soak our crops with it.
And we're stretching our supplies to the breaking point.
Will we have enough clean water to satisfy all the world's needs?

The history of human civilization is entwined with the history of the ways we have learned to manipulate water resources. The earliest agricultural communities emerged where crops could be cultivated with dependable rainfall and perennial rivers. Simple irrigation canals permitted greater crop production and longer growing seasons in dry areas. Five thousand years ago settlements in the Indus Valley were built with pipes for water supply and ditches for wastewater. Athens and Pompeii, like most Greco-Roman towns of their time, maintained elaborate systems for water supply and drainage.

As towns gradually expanded, water was brought from increasingly remote sources, leading to sophisticated engineering efforts, such as dams and aqueducts. At the height of the Roman Empire, nine major systems, with an innovative layout of pipes and well-built sewers, supplied the occupants of Rome with as much water per person as is provided in many parts of the industrial world today.

During the industrial revolution and population explosion of the 19th and 20th centuries, the demand for water rose dramatically. Unprecedented construction of tens of thousands of monumental engineering projects designed to control floods, protect clean water supplies, and provide water for irrigation and hydropower brought great benefits to hundreds of millions of people. Thanks to improved sewer systems, water-related diseases such as cholera and typhoid, once endemic throughout the world, have largely been conquered in the more industrial nations. Vast cities, incapable of surviving on their local resources, have bloomed in the desert with water brought from hundreds and even thousands of miles away. Food production has kept pace with soaring populations mainly because of the expansion of artificial irrigation systems that make possible the growth of 40 percent of the world's food. Nearly one fifth of all the electricity generated worldwide is produced by turbines spun by the power of falling water.

Yet there is a dark side to this picture: despite our progress, half of the world's population still suffers with water services inferior to those available to the ancient Greeks and Romans. As the latest United Nations report on access to water reiterated in November of last year, more than one billion people lack access to clean drinking water; some two and a half billion do not have adequate sanitation services. Preventable water-related diseases kill an estimated 10,000 to 20,000 children every day, and the latest evidence suggests that we are falling behind in efforts to solve these problems. Massive cholera outbreaks appeared in the mid-1990s in Latin America, Africa and Asia. Millions of people in Bangladesh and India drink water contaminated with arsenic. And the surging populations throughout the developing world are intensifying the pressures on limited water supplies.

The effects of our water policies extend beyond jeopardizing human health. Tens of millions of people have been forced to move from their homes--often with little warning or compensation--to make way for the reservoirs behind dams. More than 20 percent of all freshwater fish species are now threatened or endangered because dams and water withdrawals have destroyed the free-flowing river ecosystems where they thrive. Certain irrigation practices degrade soil quality and reduce agricultural productivity, heralding a premature end to the green revolution. Groundwater aquifers are being pumped down faster than they are naturally replenished in parts of India, China, the U.S. and elsewhere. And disputes over shared water resources have led to violence and continue to raise local, national and even international tensions.

At the outset of the new millennium, however, the way resource planners think about water is beginning to change. The focus is slowly shifting back to the provision of basic human and environmental needs as the top priority--ensuring "some for all, instead of more for some," as put by Kader Asmal, former minister for water affairs and forestry in South Africa. To accomplish these goals and meet the demands of booming populations, some water experts now call for using existing infrastructure in smarter ways rather than building new facilities, which is increasingly considered the option of last, not first, resort. The challenges we face are to use the water we have more efficiently, to rethink our priorities for water use and to identify alternative supplies of this precious resource.

This shift in philosophy has not been universally accepted, and it comes with strong opposition from some established water organizations. Nevertheless, it may be the only way to address successfully the pressing problems of providing everyone with clean water to drink, adequate water to grow food and a life free from preventable water-related illness. History shows that although access to clean drinking water and sanitation services cannot guarantee the survival of a civilization, civilizations most certainly cannot prosper without them.

Damage from Dams

Over the past 100 years, humankind has designed networks of canals, dams and reservoirs so extensive that the resulting redistribution of freshwater from one place to another and from one season to the next accounts for a small but measurable change in the wobble of the earth as it spins. The statistics are staggering. Before 1900 only 40 reservoirs had been built with storage volumes greater than 25 billion gallons; today almost 3,000 reservoirs larger than this inundate 120 million acres of land and hold more than 1,500 cubic miles of water--as much as Lake Michigan and Lake Ontario combined. The more than 70,000 dams in the U.S. are capable of capturing and storing half of the annual river flow of the entire country.

In many nations, big dams and reservoirs were originally considered vital for national security, economic prosperity and agricultural survival. Until the late 1970s and early 1980s, few people took into account the environmental consequences of these massive projects. Today, however, the results are clear: dams have destroyed the ecosystems in and around countless rivers, lakes and streams. On the Columbia and Snake rivers in the northwestern U.S., 95 percent of the juvenile salmon trying to reach the ocean do not survive passage through the numerous dams and reservoirs that block their way. More than 900 dams on New England and European rivers block Atlantic salmon from their spawning grounds, and their populations have fallen to less than 1 percent of historical levels. Perhaps most infamously, the Aral Sea in central Asia is disappearing because water from the Amu Darya and Syr Darya rivers that once sustained it has been diverted to irrigate cotton. Twenty-four species of fish formerly found only in that sea are currently thought to be extinct.

As environmental awareness has heightened globally, the desire to protect--and even restore--some of these natural resources has grown. The earliest environmental advocacy groups in the U.S. mobilized against dams proposed in places such as Yosemite National Park in California and the Grand Canyon in Arizona. In the 1970s plans in the former Soviet Union to divert the flow of Siberian rivers away from the Arctic stimulated an unprecedented public outcry, helping to halt the projects. In many developing countries, grassroots opposition to the environmental and social costs of big water projects is becoming more and more effective. Villagers and community activists in India have encouraged a public debate over major dams. In China, where open disagreement with government policies is strongly discouraged, protest against the monumental Three Gorges Project has been unusually vocal and persistent.

Until very recently, international financial organizations such as the World Bank, export-import banks and multilateral aid agencies subsidized or paid in full for dams or other water-related civil engineering projects--which often have price tags in the tens of billions of dollars. These organizations are slowly beginning to reduce or eliminate such subsidies, putting more of the financial burden on already strained national economies. Having seen so much ineffective development in the past--and having borne the associated costs (both monetary and otherwise) of that development--many governments are unwilling to pay for new structures to solve water shortages and other problems.

A handful of countries are even taking steps to remove some of the most egregious and damaging dams. For example, in 1998 and 1999 the Maisons-Rouges and Saint-Etienne-du-Vigan dams in the Loire River basin in France were demolished to help restore fisheries in the region. In 1999 the Edwards Dam, which was built in 1837 on the Kennebec River in Maine, was dismantled to open up an 18-mile stretch of the river for fish spawning; within months Atlantic salmon, American shad, river herring, striped bass, shortnose sturgeon, Atlantic sturgeon, rainbow smelt and American eel had returned to the upper parts of the river. Altogether around 500 old, dangerous or environmentally harmful dams have been removed from U.S. rivers in the past few years.

Fortunately--and unexpectedly--the demand for water is not rising as rapidly as some predicted. As a result, the pressure to build new water infrastructures has diminished over the past two decades. Although population, industrial output and economic productivity have continued to soar in developed nations, the rate at which people withdraw water from aquifers, rivers and lakes has slowed. And in a few parts of the world, demand has actually fallen.


United Nations Environment Program Global Environment Monitoring System's Freshwater Quality Program can be found at www.cciw.ca/gems/

VISION 21: A Shared Vision for Hygiene, Sanitation and Water Supply. Water Supply and Sanitation Collaborative Council. Available at www.wsscc.org/vision21/docs/ index.html

Related Links:

A comprehensive chronology of water- related conflicts can be found at www.worldwater.org/conflictIntro.htm 

PETER H. GLEICK is director of the Pacific Institute for Studies in Development, Environment and Security, a non-profit policy research think tank based in Oakland, Calif. Gleick co-founded the institute in 1987. He is considered one of the world's leading experts on freshwater problems, including sustainable use of water, water as it relates to climate change, and conflicts over shared water resources.

Safeguarding Our Water

Sandra Postel

If the world hopes to feed its burgeoning population, irrigation must become less wasteful and more widespread

Six thousand years ago farmers in Mesopotamia dug a ditch to divert water from the Euphrates River. With that successful effort to satisfy their thirsty crops, they went on to form the world's first irrigation-based civilization. This story of the ancient Sumerians is well known. What is not so well known is that Sumeria was one of the earliest civilizations to crumble in part because of the consequences of irrigation.

Sumerian farmers harvested plentiful wheat and barley crops for some 2,000 years thanks to the extra water brought in from the river, but the soil eventually succumbed to salinization--the toxic buildup of salts and other impurities left behind when water evaporates. Many historians argue that the poisoned soil, which could not support sufficient food production, figured prominently in the society's decline.

Far more people depend on irrigation in the modern world than did in ancient Sumeria. About 40 percent of the world's food now grows in irrigated soils, which make up 18 percent of global cropland [see illustration on page 50]. Farmers who irrigate can typically reap two or three harvests every year and get higher crop yields. As a result, the spread of irrigation has been a key factor behind the near tripling of global grain production since 1950. Done correctly, irrigation will continue to play a leading role in feeding the world, but as history shows, dependence on irrigated agriculture also entails significant risks.

Today irrigation accounts for two thirds of water use worldwide and as much as 90 percent in many developing countries. Meeting the crop demands projected for 2025, when the planet's population is expected to reach eight billion, could require an additional 192 cubic miles of water--a volume nearly equivalent to the annual flow of the Nile 10 times over. No one yet knows how to supply that much additional water in a way that protects supplies for future use.

Severe water scarcity presents the single biggest threat to future food production. Even now many freshwater sources--underground aquifers and rivers--are stressed beyond their limits. As much as 8 percent of food crops grows on farms that use groundwater faster than the aquifers are replenished, and many large rivers are so heavily diverted that they don't reach the sea for much of the year. As the number of urban dwellers climbs to five billion by 2025, farmers will have to compete even more aggressively with cities and industry for shrinking resources.

Despite these challenges, agricultural specialists are counting on irrigated land to produce most of the additional food that will be needed worldwide. Better management of soil and water, along with creative cropping patterns, can boost production from cropland that is watered only by rainfall, but the heaviest burden will fall on irrigated land. To fulfill its potential, irrigated agriculture requires a thorough redesign organized around two primary goals: cut water demands of mainstream agriculture and bring low-cost irrigation to poor farmers.

Fortunately, a great deal of room exists for improving the productivity of water used in agriculture. A first line of attack is to increase irrigation efficiency. At present, most farmers irrigate their crops by flooding their fields or channeling the water down parallel furrows, relying on gravity to move the water across the land. The plants absorb only a small fraction of the water; the rest drains into rivers or aquifers, or evaporates. In many locations this practice not only wastes and pollutes water but also degrades the land through erosion, waterlogging and salinization. More efficient and environmentally sound technologies exist that could reduce water demand on farms by up to 50 percent.


Top 10 Irrigators Worldwide

source: UN FAO AGROSTAT database 1998 

Drip systems rank high among irrigation technologies with significant untapped potential. Unlike flooding techniques, drip systems enable farmers to deliver water directly to the plants' roots drop by drop, nearly eliminating waste. The water travels at low pressure through a network of perforated plastic tubing installed on or below the surface of the soil, and it emerges through small holes at a slow but steady pace. Because the plants enjoy an ideal moisture environment, drip irrigation usually offers the added bonus of higher crop yields. Studies in India, Israel, Jordan, Spain and the U.S. have shown time and again that drip irrigation reduces water use by 30 to 70 percent and increases crop yield by 20 to 90 percent compared with flooding methods.

Sprinklers can perform almost as well as drip methods when they are designed properly. Traditional high-pressure irrigation sprinklers spray water high into the air to cover as large a land area as possible. The problem is that the more time the water spends in the air, the more of it evaporates and blows off course before reaching the plants. In contrast, new low-energy sprinklers deliver water in small doses through nozzles positioned just above the ground. Numerous farmers in Texas who have installed such sprinklers have found that their plants absorb 90 to 95 percent of the water that leaves the sprinkler nozzle.

Despite these impressive payoffs, sprinklers service only 10 to 15 percent of the world's irrigated fields, and drip systems account for just over 1 percent. The higher costs of these technologies (relative to simple flooding methods) have been a barrier to their spread, but so has the prevalence of national water policies that discourage rather than foster efficient water use. Many governments have set very low prices for publicly supplied irrigation, leaving farmers with little motivation to invest in ways to conserve water or to improve efficiency. Most authorities have also failed to regulate groundwater pumping, even in regions where aquifers are overtapped. Farmers might be inclined to conserve their own water supplies if they could profit from selling the surplus, but a number of countries prohibit or discourage this practice.

Efforts aside from irrigation technologies can also help reduce agricultural demand for water. Much potential lies in scheduling the timing of irrigation to more precisely match plants' water needs. Measurements of climate factors such as temperature and precipitation can be fed into a computer that calculates how much water a typical plant is consuming. Farmers can use this figure to determine, quite accurately, when and how much to irrigate their particular crops throughout the growing season. A 1995 survey conducted by the University of California at Berkeley found that, on average, farmers in California who used this tool reduced water use by 13 percent and achieved an 8 percent increase in yield--a big gain in water productivity.

An obvious way to get more benefit out of water is to use it more than once. Some communities use recycled wastewater [see "Waste Not, Want Not," by Diane Martindale, on page 55]. Treated wastewater accounts for 30 percent of Israel's agricultural water supply, for instance, and this share is expected to climb to 80 percent by 2025. Developing new crop varieties offers potential as well. In the quest for higher yields, scientists have already exploited many of the most fruitful agronomic options for growing more food with the same amount of water. The hybrid wheat and rice varieties that spawned the green revolution, for example, were bred to allocate more of the plants' energy--and thus their water uptake--into edible grain. The widespread adoption of high-yielding and early-maturing rice varieties has led to a roughly threefold increase in the amount of rice harvested per unit of water consumed--a tremendous achievement. No strategy in sight--neither conventional breeding techniques nor genetic engineering--could repeat those gains on such a grand scale, but modest improvements are likely.

Yet another way to do more with less water is to reconfigure our diets. The typical North American diet, with its large share of animal products, requires twice as much water to produce as the less meat-intensive diets common in many Asian and some European countries. Eating lower on the food chain could allow the same volume of water to feed two Americans instead of one, with no loss in overall nutrition.

Reducing the water demands of mainstream agriculture is critical, but irrigation will never reach its potential to alleviate rural hunger and poverty without additional efforts. Among the world's approximately 800 million undernourished people are millions of poor farm families who could benefit dramatically from access to irrigation water or to technologies that enable them to use local water more productively.

Most of these people live in Asia and Africa, where long dry seasons make crop production difficult or impossible without irrigation. For them, conventional irrigation technologies are too expensive for their small plots, which typically encompass fewer than five acres. Even the least expensive motorized pumps that are made for tapping groundwater cost about $350, far out of reach for farmers earning barely that much in a year. Where affordable irrigation technologies have been made available, however, they have proved remarkably successful.

I traveled to Bangladesh in 1998 to see one of these successes firsthand. Torrential rains drench Bangladesh during the monsoon months, but the country receives very little precipitation the rest of the year. Many fields lie fallow during the dry season, even though groundwater lies less than 20 feet below the surface. Over the past 17 years a foot-operated device called a treadle pump has transformed much of this land into productive, year-round farms.

To an affluent Westerner, this pump resembles a StairMaster exercise machine and is operated in much the same way. The user pedals up and down on two long bamboo poles, or treadles, which in turn activate two steel cylinders. Suction pulls groundwater into the cylinders and then dispenses it into a channel in the field. Families I spoke with said they often treadled four to six hours a day to irrigate their rice paddies and vegetable plots. But the hard work paid off: not only were they no longer hungry during the dry season, but they had surplus vegetables to take to market. Costing less than $35, the treadle pump has increased the average net income for these farmers--which is often as little as a dollar a day--by $100 a year. To date, Bangladeshi farmers have purchased some 1.2 million treadle pumps, raising the productivity of more than 600,000 acres of farmland. Manufactured and marketed locally, the pumps are injecting at least an additional $350 million a year into the Bangladeshi economy.

In other impoverished and water-scarce regions, poor farmers are reaping the benefits of newly designed low-cost drip and sprinkler systems. Beginning with a $5 bucket kit for home gardens, a spectrum of drip systems keyed to different income levels and farm sizes is now enabling farmers with limited access to water to irrigate their land efficiently. In 1998 I spoke with farmers in the lower Himalayas of northern India, where crops are grown on terraces and irrigated with a scarce communal water supply. They expected to double their planted area with the increased efficiency brought about by affordable drip systems.

Bringing these low-cost irrigation technologies into more widespread use requires the creation of local, private-sector supply chains--including manufacturers, retailers and installers--as well as special innovations in marketing. The treadle pump has succeeded in Bangladesh in part because local businesses manufactured and sold the product and marketing specialists reached out to poor farmers with creative techniques, including an open-air movie and village demonstrations. The challenge is great, but so is the potential payoff. Paul Polak, a pioneer in the field of low-cost irrigation and president of International Development Enterprises in Lakewood, Colo., believes a realistic goal for the next 15 years is to reduce the hunger and poverty of 150 million of the world's poorest rural people through the spread of affordable small-farm irrigation techniques. Such an accomplishment would boost net income among the rural poor by an estimated $3 billion a year.

Over the next quarter of a century the number of people living in water-stressed countries will climb from 500 million to three billion. New technologies can help farmers around the world supply food for the growing population while simultaneously protecting rivers, lakes and aquifers. But broader societal changes--including slower population growth and reduced consumption--will also be necessary. Beginning with Sumeria, history warns against complacency when it comes to our agricultural foundation. With so many threats to the sustainability and productivity of our modern irrigation base now evident, it is a lesson worth heeding.

Further Information:

Salt and Silt in Ancient Mesopotamian Agriculture. Thorkild Jacobsen and Robert M. Adams in Science, Vol. 128, pages 1251–1258; November 21, 1958.

Pillar of Sand: Can the Irrigation Miracle Last? Sandra Postel. W. W. Norton, 1999.

Groundwater in Rural Development. Stephen Foster et al. Technical Paper No. 463. World Bank, Washington, D.C., 2000.

Irrigation and land-use databases are maintained by the United Nations Food and Agriculture Organization at http://apps.fao.org

The Author

SANDRA POSTEL directs the Global Water Policy Project in Amherst, Mass., and is a visiting senior lecturer in environmental studies at Mount Holyoke College. She is also a senior fellow of the Worldwatch Institute, where she served as vice president for research from 1988 to 1994.

How We Can Do It

Diane Martindale and Peter H. Gleick

Approach 1: Seek New Sources

A water-covered planet facing a water crisis seems paradoxical. And yet that is exactly the reality on planet Earth, where 97 percent of the water is too salty to quench human thirst or to irrigate crops. Tackling water-shortage issues with desalination--drawing fresh, drinkable water out of salty seawater--is common in the desert nations of the Middle East, the Caribbean and the Mediterranean. But as the cost of desalination drops and the price and demand for water climb, countries in temperate regions are turning more and more to the sea.

Large-scale desalination facilities are even turning up in the U.S., one of the world's most water-rich countries. As part of an ambitious plan to reduce pumping from depleted underground aquifers, water officials in the Tampa Bay, Fla., area are contracting the construction of a desalination plant capable of producing 25 million gallons of desalted water a day. They are relying on desalination to supplement the region's future water demands. Houston is also looking at desalinating water from the Gulf of Mexico to keep from going dry.

People have been pulling freshwater out of the oceans for centuries using technologies that involve evaporation, which leaves the salts and other unwanted constituents behind. Salty source water is heated to speed evaporation, and the evaporated water is then trapped and distilled. This process works well but requires large quantities of heat energy, and costs have been prohibitive for nearly all but the wealthiest nations, such as Kuwait and Saudi Arabia. (One exception is the island of Curaçao in the Netherlands Antilles, which has provided continuous municipal supplies using desalination since 1928.) To make the process more affordable, modern distillation plans recycle heat from the evaporation step.

A potentially cheaper technology called membrane desalination may expand the role of desalination worldwide, which today accounts for less than 0.2 percent of the water withdrawn from natural sources. Membrane desalination relies on reverse osmosis--a process in which a thin, semipermeable membrane is placed between a volume of saltwater and a volume of freshwater. The water on the salty side is highly pressurized to drive water molecules, but not salt and other impurities, to the pure side. In essence, this process pushes freshwater out of saltwater.

Most desalination research over the past few years has focused on reverse osmosis, because the filters and other components are much smaller than the evaporation chambers used in distillation plants. Reverse-osmosis plants are also more compact and energy-efficient.

Although reverse-osmosis plants can offer energy savings, the earliest membranes, made from either polyamide fibers or cellulose acetate sheets, were fragile and had short life spans, often no longer than three years. These materials are highly susceptible to contaminants in the source water--particularly chlorine, which hardens the membranes, and microbes, which clog them. Pretreatment regimes, such as filtering out sediments and bacteria, must be extremely rigorous. A new generation of so-called thin composite membranes, made from polyamide films, promises to eliminate these problems. Though still susceptible to contamination, these new membranes are sturdier, provide better filtration and may last up to 10 years.

Technical performance is important, but it alone does not drive the adoption of desalination as a source of clean water. With or without technical improvements, the market for desalination equipment will very likely show healthy growth in the next 10 years as cities and other consumers realize the potential and favorable economics of existing equipment, according to James D. Birkett, who runs West Neck Strategies, a private desalination consulting company based in Nobleboro, Me.

Hundreds of suppliers are already selling many thousands of pieces of equipment annually. These desalination units range in capacity from a few gallons a day (small emergency units for life rafts) to several million gallons a day (municipal systems). "So confident are the suppliers that they enter into long-term contracts with their customers," Birkett says, "thus assuming themselves the risks of performance and economics." The desalination plant on Tampa Bay, scheduled to be operational by the end of 2002, will be funded and operated in such a manner.

Today the best estimate is that about 1 percent of the world's drinking water is supplied by 12,500 desalination plants. No doubt, this is only the beginning. In the future, the water in your glass may have originated in the seas. --Diane Martindale

Approach 2: Redistribute Supplies

Pipelines make it possible to move freshwater cheaply over vast distances of land. If only the same were possible over the oceans. Dragging waterproof plastic or fabric containers behind tugboats may be the answer.

Beginning in 1997, the English company Aquarius Water Trading and Transportation Ltd has towed water from mainland Greece to nearby resort islands in enormous polyurethane bags, helping the tourist destinations deal with increased demand for drinking water during the peak season. Another company, Nordic Water Supply in Oslo, Norway, has made similar deliveries from Turkey to northern Cyprus using their own fabric containers.

The seemingly far-fetched concept of water bags was born in the early 1980s out of the desire to move large amounts of water more cheaply than modified oil tankers can do. For many years, tankers and barges have been making deliveries to regions willing to pay premium prices for small amounts of freshwater, such as the Bahamas, Cyprus and other islands with inadequate sources. Tankers have also supplied water during short-term droughts and disasters such as the 1995 Kobe earthquake in Japan.

Aquarius has manufactured eight 790-ton bags and two 2,200-ton versions; the latter hold about half a million gallons of water each. Aquarius has also developed models that are 10 times larger than the ones in use today, and last year Nordic began manufacturing bags that can hold nearly eight million gallons.

Water bags could offer a less expensive alternative to tankers--bags in the Aquarius fleet cost anywhere from $125,000 to $275,000--but some technical problems remain. In particular, making such large bags that are capable of withstanding the strains of an ocean voyage is difficult. For freshwater deliveries to the Greek isles and to Cyprus, bags need be dragged no farther than 60 miles. The piping systems needed to connect the bags to water supplies on land can be built from existing technology, but bags have ripped during transport on several occasions.

A third water-bag inventor, Terry G. Spragg of Manhattan Beach, Calif., is solving the problems of both volume and towing in a different way. With the support of privately hired scientists and consultants, Spragg has patented specialized zippers, with teeth more than an inch long, that can link water bags like boxcars. He has demonstrated the technology but has yet to sell it for commercial use.

Thus far this technology has been used only for freshwater deliveries to emergency situations and to extremely water-scarce coastal regions with a reliable demand for expensive water. But for some communities with no other option, water bags may offer a new and clever solution. --Peter H. Gleick

Approach 3: Reduce Demand

New York City is a metropolis of flamboyant excess, except when it comes to water. No one would suspect it, but the Big Apple has clamped down on water wasters, and after 10 years of patching leaky pipes and replacing millions of water-guzzling toilets, the city is now saving billions of gallons of water every year.

Back in the early 1990s New York City faced an imminent water shortage, and it was getting worse with every flush, shower and tooth brushing. With an influx of new residents and an increase in the number of drought years, the city needed to find an extra 90 million gallons of water a day--about 7 percent of the city's total water use. Instead of spending nearly $1 billion for a new pumping station along the Hudson River, city officials opted for a cheaper alternative: reduce the demand on the current water supply, which was piped in from the Catskill Mountains.

Officials knew that persuading New Yorkers to go green and conserve water would require some enticement--free toilets. The city's Department of Environmental Protection (DEP) stepped in with a three-year toilet rebate program, which began in 1994. With a budget of $295 million for up to 1.5 million rebates, the ambitious scheme set out to replace one third of the city's inefficient toilets--those using more than five gallons of water per flush--with water-saving models that do the same job with only 1.6 gallons per flush. With the rebate program, the DEP hoped to meet the largest part of its water-savings goal.

New Yorkers embraced the plan. Some 20,000 applications arrived within three days of its start. By the time the program ended in 1997, low-flow toilets had replaced 1.33 million inefficient ones in 110,000 buildings. The result: a 29 percent reduction in water use per building per year. The DEP estimates that low-flow toilets save 70 million to 90 million gallons a day citywide--enough to fill about 6,700 Olympic-size swimming pools.

But more efficient flushes weren't enough. The toilet rebate program happened concurrently with the city's water audit program, which continues today. For much of the city's history, the amount building owners paid for water was based on the size of their property. Following a law passed in 1985, however, the city began keeping tabs on water use and charging accordingly. The law dictated that water meters be installed during building renovations, and the same requirement was applied to construction of new homes and apartments beginning in 1988. As of 1998, all properties in the city must be metered. Homeowners who want to keep their water bills down under the new laws can request a free water-efficiency survey from Volt VIEWtech, the company that oversees the city's audit program. Inspectors check for leaky plumbing, offer advice on retrofitting with water-efficient fixtures and distribute free faucet aerators and low-flow showerheads. Low-flow showerheads use about half as much water as the old ones, and faucet aerators, which replace the screen in the faucet head and add air to the spray, can lower the flow of water from four gallons a minute to less than one gallon a minute. Volt VIEWtech has made several hundred thousand of these inspections, saving an estimated 11 million gallons of water a day in eliminated leaks and increased efficiency.

In efforts to save even more water, New York City has gone outside the home and into the streets. Water officials have installed magnetic locking caps on fire hydrants to keep people from turning them on in the summer. The city is also keeping an eye underground by using computerized sonar equipment to scan for leaks along all 32.6 million feet (6,174 miles) of its water mains.

Although the city's population continues to grow, per person water use in New York dropped from 195 to 169 gallons a day between 1991 and 1999. From all indications, this trend is following its upward path. Water conservation works. And New Yorkers are proving that every flush makes a difference. --D.M.

Approach 4: Recycle

In the world's arid regions, even sewage water cannot be thrown away Namibia is the driest African country south of the Sahara Desert. Blistering heat evaporates water faster than rains can rejuvenate the parched landscape, and there are no year-round rivers. Residents of the capital city, Windhoek, must do more than just conserve water to secure a permanent supply. They must reuse the precious little they have.

By the end of the 1960s, most underground aquifers and reservoirs on seasonal rivers near Windhoek had been tapped dry by the capital's burgeoning population, which has grown from 61,000 to more than 230,000 in the past 30 years. Transporting water from the closest permanent river, the Okavango--some 400 miles away--was too expensive. This crisis inspired city officials to implement a strict water conservation scheme that includes reclaiming domestic sewage and raising it once again to drinkable standards.

The city's first reclamation plant, initially capable of producing only 460 million gallons of clean water per year when it went on line in 1968, is now pumping out double that amount--enough to provide about 23 percent of the city's yearly water demands. Officials hope to boost that supply number to 51 percent with an upcoming facility now under construction.

To make wastewater drinkable, it must undergo a rigorous cleaning regimen. First, large solids are allowed to settle out while biofilters remove smaller organic particles. Advanced treatments remove ammonia, and carbon and sand filters ensure that the last traces of dissolved organic material are eliminated. The final step is to purify the water by adding chlorine and lime. To guarantee a safe drinking supply, the reclaimed water is tested once a week for the presence of harmful bacteria, viruses and heavy metals. (Industrial effluent laden with toxic chemicals is diverted to separate treatment plants.) Compared with local freshwater sources, the reclaimed water is equal or better in quality.

Despite 32 years of access to high-quality recycled water, the residents of Windhoek still doggedly oppose its use for personal consumption. For this reason, most of this purified wastewater irrigates parks and gardens. But sometimes people don't have a choice about their water source. In times of peak summer demand or during emergencies such as drought, local freshwater reservoirs are strained, and Windhoek relies heavily on treated effluent to boost supply. During the drought of 1995, for instance, reclaimed water accounted for more than 30 percent of the clean water piped into homes.

Officials hope to bolster support for the recycling program through enhanced public education--like letting the word slip that besides irrigating the city's greenery, treated wastewater is the secret ingredient in the prized local brew. --D.M.

Further Information:

For a list of the dos and don'ts about home water conservation, visit the New York City Department of Environmental Protection on the World Wide Web at www.ci.nyc.ny.us/dep 

The Authors

DIANE MARTINDALE is a science writer based in New York City who says she will trade her bottle of Evian for a taste of the sea anytime.

PETER H. GLEICK is the author of "Making Every Drop Count," in this special report.

Continuing Conflict Over Fresh Water

Peter H Gleick

Myths, legends and written histories reveal repeated controversy over freshwater resources since ancient times. Scrolls from Mesopotamia, for instance, indicate that the states of Umma and Lagash in the Middle East clashed over the control of irrigation canals some 4,500 years ago.

Throughout history, water has been used as a military and political goal, as a weapon of war and even as a military target. But disagreements most often arise from the fact that water resources are not neatly partitioned by the arbitrary political borders set by governments. Today nearly half of the land area of the world lies within international river basins, and the watersheds of 261 major rivers are shared by two or more countries. Overlapping claims to water resources have often provoked disputes, and in recent years local and regional conflicts have escalated over inequitable allocation and use of water resources.

A small sampling of water conflicts that occurred in the 20th century demonstrates that treaties and other international diplomacy can sometimes encourage opposing countries to cooperate--but not always before blood is shed. The risk of future strife cannot be ignored: disputes over water will become more common over the next several decades as competition for this scarce resource intensifies. --P.H.G.

U.S. 1924

Local farmers dynamite the Los Angeles aqueduct several times in an attempt to prevent diversions of water from the Owens Valley to Los Angeles.

India and Pakistan 1947 to 1960

Partitioning of British India awkwardly divides the waters of the Indus River valley between India and Pakistan. Competition over irrigation supplies incites numerous conflicts between the two nations; in one case, India stems the flow of water into Pakistani irrigation canals. After 12 years of World Bank–led negotiations, a 1960 treaty helps to resolve the discord.

Egypt and Sudan 1958

Egypt sends troops into contested territory between the two nations during sensitive negotiations concerning regional politics and water from the Nile. Signing of a Nile waters treaty in 1959 eases tensions.

Israel, Jordan and Syria 1960s and 1970s

Clashes over allocation, control and diversion of the Yarmouk and Jordan rivers continue to the present day.

South Africa 1990

A pro-apartheid council cuts off water to 50,000 black residents of Wesselton Township after protests against wretched sanitation and living conditions.

Iraq 1991

During the Persian Gulf War, Iraq destroys desalination plants in Kuwait. A United Nations coalition considers using the Ataturk Dam in Turkey to shut off the water flow of the Euphrates River to Iraq. <

India 1991 to present

An estimated 50 people die in violence that continues to erupt between the Indian states of Karnataka and Tamil Nadu over the allocation of irrigation water from the Cauvery River, which flows from one state into the other.

Yugoslavia 1999

NATO shuts down water supplies in Belgrade and bombs bridges on the Danube River, disrupting navigation.

Where will the water be?

The total amount of water withdrawn globally from rivers, underground aquifers and other sources has increased ninefold since 1900 (chart). Water use per person has only doubled in that time, however, and it has even declined slightly in recent years. Despite this positive trend, some experts worry that improvements in water-use efficiency will fail to keep pace with projected population growth. Estimated annual water availability per person in 2025 (map) reveals that at least 40 percent of the world's 7.2 billion people may face serious problems with agriculture, industry or human health if they must rely solely on natural endowments of freshwater. Severe water shortages could also strike particular regions of water-rich countries, such as the U.S. and China.

People's access to water also depends on factors not reflected here, such as political and economic conditions, changing climate patterns and available technology. --P.H.G.

More than 450,000 gallons/person. Problems limited to particular regions and seasons for 59.3% of world.

Annual Global Water Withdrawals

  Some areas prone to severe water shortages
260,000 to 450,000 gallons/person. Constraints on agricultural food supplies for 32.6% of world population.
130,000 to 260,000 gallons/person. Persistent restrictions on agriculture and industry for 5.3% of world population.
Less than 130,000 gallons/person. Potentially serious threat to agriculture, industry and human health for 2.8% of world population.

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