10/7/2016

1/6

Print

WEEK FOUR: WHAT ARE THE CHALLENGES OF MANAGING EARTH'S FRESH WATER? | ESSAY TWO

Sources and Uses of Fresh Water

by Eleanor Sterling, Nora Bynum, and Erin Vintinner

In the fall of 2007, Nora Bynum, one of the authors, was shocked to discover that the reservoir near her North Carolina home had been reduced

to a small pond, and that the shoreline had receded by hundreds of feet. The dire warnings about the drought across the southeastern U.S.

—"Only 15 more days of municipal water left!" "Only 7 more days of water left!"—had come home. Talk of water conservation was on

everyone's lips. Fast-forward to the abnormally wet spring of 2009, which brought reservoir levels back to normal. Conservation—not to

mention planning for future droughts—disappeared from the conversation. What will it take for us to consider lasting changes?

Dry and Populated

Deserts (visible in tan in this true-color satellite view) today cover about 25 percent of Earth's surface. More than 500 million people live in

deserts and dry lands. ©NASA GSFC

Enlarge image »

We can survive weeks without food, but not without water. All species that are dependent on fresh water must share a tiny, finite fraction of

Earth's water. Though locally renewable, fresh water is not evenly distributed across the planet, throughout the seasons, or from year to year.

Some areas in the country of Colombia, for example, receive up to 7.6 meters (almost 25 feet) of rainfall a year, while Chile's Atacama Desert

is a virtually rainless plateau. India gets an overwhelming majority of its rainfall during the four-month summer monsoon. In the Galápagos

archipelago, rainfall can vary widely between years within and between islands. One island received over 3.2 meters (10 feet) of rain from 1982

to 1983, when its previous average was 500 mm (20 inches) a year.

Global human freshwater use increased by about 20 percent per decade between 1960 and 2000 to meet rising industrial, domestic, and

agricultural demand. Ingenuity now allows close to 2 billion people—nearly one-third of the world's population—to live in areas where water

is relatively scarce, or where it's salty or frozen.

10/7/2016

2/6

Water Use

This graph shows global water consumption from 1900 to 2010 in cubic kilometers per year, broken down by usage. ©AMNH

Enlarge image »

Water Distribution

This chart shows the distribution of water on Earth. Only 2.5 percent of all water is fresh, most of which is locked up in glaciers and ice caps.©AMNH

Enlarge image »

A Closer Look at Water Stress and Scarcity

10/7/2016

3/6

The minimum amount of water needed to meet the basic needs of drinking, cooking, and hygiene—while still far below the level needed toensure health and well-being—is between 20 liters (five gallons) and 50 liters (13 gallons) of clean water per person per day. Yet many peopleroutinely have access to less than five liters (1.3 gallons) a day. Clean, relatively convenient water is unavailable to half the rural population of27 developing countries—about 900 million people.

A country's total renewable water resources consist of its flowing and standing water supplies, minus any that may be required by treaty toleave the country or that must remain for navigation, hydropower, or to maintain ecosystem health. Nonrenewable groundwater, which is slowto recharge, supports an estimated 1.5 billion to 3 billion people globally. Forty percent of industrial demand and 20 percent of irrigationdemand are also met by groundwater. Despite its importance, groundwater is rarely used sustainably.

Hydrologists define "water-stressed" countries as those with renewable supplies of 1,000 to 1,700 cubic meters (264,000 to 449,000 gallons, orabout one-half to two-thirds the volume of an Olympic-size swimming pool) per person per year. This is not enough water to grow crops, soself-sufficiency becomes difficult or impossible. In "water-scarce" countries with supplies below 1,000 cubic meters per person per year, there'stypically not enough water available to meet the demands of industries, cities, and households, dilute pollution, satisfy other ecologicalfunctions, and grow sufficient food. In much of the world, population growth and the overexploitation and contamination of water resources arewidening the gap between what's available and what's needed. By 2025, 2.8 billion people in 48 countries will face water stress or scarcity ifour water use continues unchanged.

Water Stress

This map takes into account environmental water needs, which is the amount of water needed to keep freshwater ecosystems in a fair condition.Orange and yellow areas show where environmental water needs are not being satisfied because too much water is already being withdrawn forother uses, and where human access to water is limited because of financial constraints. ©International Water Management Institute / AMNH

Enlarge image »

What Does Scarcity Mean for People?Caught between finite and increasingly polluted water supplies on the one hand, and rapidly rising demand from human population growth anddevelopment on the other, we face difficult choices. When water is dammed, diverted, and pumped unsustainably, overconsumption can causelong-term environmental damage. Competition for fresh water can breed social and political tensions since bodies of water do not respectpolitical boundaries. Scarcity in key agricultural regions could threaten global food production, and in metropolitan areas could adversely affectpublic and economic health.

In urban areas, residents who lack water hookups must often rely on expensive bottled or trucked-in water. Piped water systems are rare in ruralareas. Two-thirds of the world's population, the majority in developing countries, gets their water from public standpipes, community wells,surface water such as rivers and lakes, or collected rainwater. If there's no infrastructure, people have to travel longer and longer distances assupply dwindles. This has tremendous social costs, often borne by the women and girls most often tasked with bringing water back to the

10/7/2016

4/6

home. For instance, during the dry season, water gatherers in some regions of rural Africa must walk as far as 10 kilometers (more than sixmiles) a day to reach water, which leaves little time to attend school.

The Aral Sea

Once the world's fourth-largest saline body of water, the Aral Sea left the local fishing industry high and dry when the former Soviet Union(now Uzbekistan) aimed to irrigate the desert for cotton production. ©Flickr / Miles Hunter

Enlarge image »

What Does Scarcity Mean for Ecosystems?Since water plays such a significant role in sustaining natural systems, scarcity has wide-ranging effects. An adequate flow of good-qualitywater (called "environmental" flows) is needed to maintain the health of inland water systems as well as estuaries and deltas. The reverse is alsotrue: Healthy inland water systems generate and maintain adequate flows of good-quality water and provide essential services. Water scarcitythreatens these services.

The effects of water scarcity on humans and ecosystems are closely linked, limiting economic and social development in many countries.However, many projects undertaken to increase access to water fail to consider their harmful effects on ecosystem services. For example, whenrivers are diverted, flows may no longer be able to sustain fisheries.

Central Asia's Aral Sea is an extreme example of what happens to an ecosystem when water flow diminishes. When the two main incomingrivers, the Syr and the Amu, were diverted, this inland sea shrank by more than 75 percent, exposing miles of arid desert. Some 5 millionpeople in the region are now exposed to winds that carry millions of tons of toxic dust (containing salts and pesticides from agricultural runoff)per year from the exposed lakebed. This affects regional agriculture and human health. The remaining lake water is so salty that 20 of its 24 fishspecies have died out, and the annual catch has dropped from 50,000 tons (100 million pounds) in the 1950s to practically zero today.

The Challenge of IrrigationToday, 40 percent of the world's food is grown in areas too dry for rainfall alone to sustain crops. Irrigation consumes more water than anyother human activity, and less than half of the water actually makes it to crop roots. Many farmers still irrigate the way their ancestors did 5,000years ago, by flooding or channeling water by gravity across their cropland. Water is lost as it's distributed, though some flows back into nearbywater bodies or contributes to aquifer recharge. In hot climates, much of the water evaporates.

The concept of "water productivity" is now widely used to measure performance in agricultural water use, reducing waste through practicessuch as cropland leveling or drip irrigation, which applies water directly to crop roots. But even productive irrigation contributes tounsustainable patterns. Agricultural water use increased fivefold in the 20th century, with a rapid rise at mid-century with the dawn of the greenrevolution. Productive irrigation may enable farmers to grow several crops a year, but this requires more water, pesticides, and fertilizers.

What About Water for Industries and Cities?Many industries are water-intensive, using water for cleaning, heating, cooling, generating steam, transporting dissolved substances, as a rawmaterial, and as a constituent of the product itself. For example, making 100 sheets of paper can require as much as 1,000 liters (264 gallons orfive full bathtubs) of water. Regulations and cost-cutting measures have reduced the amount of water needed for production, but this variesthroughout the world. Producing a ton of steel in China, for example, consumes up to 56 cubic meters (almost 15,000 gallons) of water,compared to an average of less than 6 cubic meters (1,600 gallons) in Germany and Japan.

While an average of only 8 percent of the world's water goes to domestic and municipal purposes, it's critical to human health anddevelopment. Leaks out of water mains, pipes, and faucets can waste water before it reaches city dwellers. In Spain, for example, around 20percent of the total municipal water supply is lost to leaks. But convenient access to running water can eliminate the incentive to conserve.

10/7/2016

5/6

Cuba's Modern Agriculture Boom

In the 1980s, when support from the Soviet Union was no longer available, Cuba had to start rethinking its approach to agriculture. Today,Cuba provides its citizens with organic and sustainable produce that relies on modern irrigation techniques. ©Organic Seed Alliance / BrianSnyder

Enlarge image »

Virtual WaterWater used in the production of crops or manufactured goods, known as virtual water, is closely linked to water scarcity, especially in dry areas."Thirsty crops" like wheat and cotton have high virtual water content. Since animals consume food and water, it takes 2,300 liters (600 gallons)of water to produce 150 grams (one-third of a pound) of beef for a hamburger. Virtual water content varies between places, depending onclimate and technology. For example, the global average virtual water content for white rice is 3.4 cubic meters (almost 900 gallons, almost 20full bathtubs worth) per kilogram, but it's more for rice grown in India or Brazil (4.2 cubic meters/kilogram and 4.6 cubic meters/kilogram,respectively). Industrial products also contain virtual water, though the amounts vary depending on the production method.

When a country exports a water-intensive product, it is draining the country of its water resources. According to the U.N., between 15 and 20percent of water used by humans is exported. The amount of international virtual water transfer is estimated to equal or exceed the CongoRiver's annual runoff (the total volume of water flows from precipitation and groundwater combined). Kenya, for example, is using the watersof Lake Naivasha to grow roses for export to Europe.

How Much Virtual Water Is in a Cup of Coffee?

Take a Drink

How much virtual (or direct) water is in what you drink? ©AMNH

Almost every product that we use contains virtual water. Coffee provides one interesting example of the many ways in which water is used tomake a product. Coffee plants are nourished by rainwater and irrigation. Harvested cherries are then pulped to extract beans that are fermentedand washed in water. One cup, on average, contains 140 liters (37 gallons) of virtual water—many times the volume of the liquid in the cup!Coffee consumes about 2 percent of all the water used to grow crops worldwide. The Netherlands, for example, has a coffee-related waterfootprint of 2.6 billion cubic meters (about 690 billion gallons) of water per year—equivalent to almost 4 percent of the annual flow of theRhine River.

Enlarge image »

10/7/2016

6/6

What Does the Future Hold?

Given current demands, how can we provide for the needs of another 2 billion to 3 billion people in the coming years? Like the people in

drought-stricken southeastern U.S. states in 2007, we need to change existing perceptions of how water is valued and managed. How do we

manage freshwater systems sustainably while maintaining ecosystem health?

Related Links

Water Footprint »

See how much water it takes to produce agricultural products: from bread and cotton to rice and sugar.

International Water Management Institute »

Learn about several important themes of water research, including productive water use, water quality, and water access.

Rodale Institute: Cuba »

An article about the development of an international model for sustainable agriculture techniques, including modern irrigation and organic

seed, and its proving ground in Havana, Cuba.

How Much Water Do You Use? »

Download this infographic that explains direct and virtual use of water in our everyday lives. Then you can calculate your water footprint.