Applied Sciences

Section 5.3 Global Water Use and Demand

Who Uses Water (and How Much) Globally, agriculture is the largest user of water, accounting for about 70% of all extractive water uses. However, this global average masks wide variations in water consumption by sec- tor and in the overall amounts of water consumed. For example, in Africa and Asia agriculture accounts for over 80% of all water use, whereas in more industrialized countries of Europe, only 20% goes to agriculture while 60% goes to industry (Food and Agriculture Organiza- tion of the United Nations, 2016). Figure 5.5 shows a breakdown of average water use in the United States. But even within the United States, there can be significant variations in these figures. Most water use in the more industrialized and populated regions of the Northeast is for power plants, industry, and residential uses. In drier regions of the West and Southwest, over 80% of water use is for agriculture (Dieter et al., 2018).

Per capita levels of water consumption also vary widely among different regions of the world (see Table 5.1). This is partly a result of water supply and the infrastructure needed to deliver that water to people when and where they need it. It’s also a function of factors like standard of living, how efficiently water is used in that country, the kinds of economic activities under- taken there, and the food choices people make. Water consumption generally increases with standard of living, and countries that produce highly water-intensive products like cotton and beef tend to have higher rates of per capita water use. This is one of the reasons why the United States and Australia, both big producers and consumers of beef, have some of the high- est rates of per capita water consumption in the world.

Apply Your Knowledge: What Is the Environmental Impact of Nonconsumptive Water Use? (continued)

When industries like BNPP impact the environment by adding heat, we call it thermal pollution. Thermal pollution affects both freshwater and marine ecosystems like the one in Ilha Grande Bay. According to a recent study, the Mississippi River absorbs more heat from nonconsumptive water use than any other river in the world. Meanwhile, the Rhine River in Europe experiences the most significant temperature increases from thermal pollution of any major river. Coal and nuclear power plants serve as the pollution sources in both cases (Raptis, Van Vliet, & Pfister, 2016).

Thermal pollution is an example of a 21st-century environmental problem. Like many of our most pressing issues, it is the result of complex human and environmental systems that interact in sometimes unexpected ways. It demonstrates that we need to do more than just reduce material flows if we want a sustainable future. We also need to understand systems holistically and consider all the environmental factors that allow life to thrive.

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Section 5.3 Global Water Use and Demand

Figure 5.5: Water use in the United States

These pie charts show average water use across the United States, but the breakdown can vary significantly by region.

Source: Adapted from “Summary of Estimated Water Use in the United States in 2015,” by US Geological Survey, 2018 (https://pubs.usgs .gov/fs/2018/3035/fs20183035.pdf); adapted from “Residential End Uses of Water, Version 2,” by US Environmental Protection Agency and Water Research Foundation, 2016 (https://www.waterrf.org/research/projects/residential-end-uses-water-version-2).

Water use in the United States, by category (2015)

Household water use in the United States, by activity (2016)

Agriculture 37.4%

Electric power 41.4%

Aquaculture 2.3%

Industry and mining 5.8%

Residential and

commercial 13.1%

Toilet 24%

Shower 20%Faucet

19%

Other 8%

Leak 12%Clothes

washer 17%

Table 5.1: Annual per capita water use around the world (1996–2005)

Low (<1,000 m3) Medium (1,000–2,000 m3) High (>2,000 m3)

Bangladesh 769 South Africa 1,255 Israel 2,303

Rwanda 821 Japan 1,379 Australia 2,315

Nicaragua 912 Thailand 1,407 Canada 2,333

Malawi 936 Germany 1,426 Spain 2,461

Guatemala 983 France 1,786 United States 2,842

Note. 1 m3 = 264 gallons.

Source: Data from “The Water Footprint of Humanity, by A. Y. Hoekstra and M. M. Mekonnen, 2012, Proceedings of the National Academy of Sciences, 109 (https://waterfootprint.org/en/resources/waterstat/national-water-footprint-statistics).

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Section 5.3 Global Water Use and Demand

The example of beef illustrates an important concept known as virtual water, or embodied water. We may not think about it, but just about every item we use or consume required water to produce. In terms of food items, for example, it takes roughly 15,415 liters (4,072 gallons) of water to produce one kilogram of beef, and 1,608 liters (425 gallons) of water to produce enough wheat for a kilogram of bread (see Figure 5.6). But water is also used to produce nonfood items as well. For example, it takes roughly 5,400 liters (1,427 gallons) of water to produce one pair of jeans. For comparison, we use about 75 to 100 liters (20 to 26 gallons) of water for an average 10-minute shower.

Figure 5.6: Virtual water

This graph illustrates the liters of water needed to produce a kilogram of each of these food items. The amount of water required to produce the food we eat is not always obvious.

Source: Data from “Product Gallery,” by Water Footprint Network, n.d. (https://waterfootprint.org/en/resources/interactive-tools/product -gallery/).

287

560

790

822

1,020

1,220

1,420

1,608

3,178

3,300

4,325

5,988

15,415

17,196

18,900

Potatoes

Oranges

Bananas

Apples

Milk

Corn

Beer

Bread

Cheese

Eggs

Chicken

Pork

Beef

Chocolate

Coffee

Liters of water

20,00010,000 15,0005,0000

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Section 5.3 Global Water Use and Demand

The virtual water concept helps illustrate how consumption decisions made in one location can impact water supply and management issues in another. In recent years California has been experiencing severe droughts and water shortages, and yet this state alone produces over a third of America’s vegetables and two thirds of its fruits and nuts. It’s estimated that the average American consumes over 1,100 liters (290 gallons) of California water every week by eating food products grown there (Buchanan, Keller, & Park, 2015). The virtual water concept also makes even clearer the problem of food loss and waste discussed in Chapter 4. Every time we waste food, we are also wasting all the water (and energy; see Chapter 7) used in the production of that food.

Challenges of Meeting Water Demand Many regions of the world are already experiencing, or will soon experience, serious chal- lenges in meeting their water needs. Water scarcity refers to a situation in which there is a physical, volume-based lack of water. It’s estimated that close to 700 million people in 43 countries around the world currently experience water scarcity and that this number could more than double in the next decade (United Nations Department of Economic and Social Affairs [UNDESA], n.d.b). Water stress, in contrast, is a broader term that includes physi- cal scarcity as well as issues of water quality and the accessibility or affordability of clean water supplies. Over 1 billion people are currently experiencing water stress, and this figure could grow as high as 4 billion in the decades ahead unless more effective and efficient water management practices are implemented (UNDESA, n.d.b). Later sections in this chapter will highlight ways we can address water scarcity and stress, as well as challenges related to water quality. Before that, however, let’s have a look at some areas where meeting water demand is proving difficult.

Water Rationing in South Africa One of the most high-profile and recent examples of water scarcity is playing out in the city of Cape Town, South Africa. Cape Town is a modern, bustling metropolis and a major tourist destination located at the southern tip of the African continent. It has a population (4 million) and climate similar to Los Angeles in Southern California.

After 3 years of severe drought and poor water management decisions, the city began to warn residents and businesses in late 2017 of “Day Zero,” the day when municipal water would

Learn More: Your Water Footprint

There are a number of sources that allow you to explore and calculate your “water footprint” in different ways.

• https://waterfootprint.org/en • https://www.watercalculator.org • https://water.usgs.gov/edu/activity-percapita.html

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Section 5.3 Global Water Use and Demand

be completely cut off and water would be available only through centralized distribu- tion points. Cape Town was set to become the first modern major city in the world to run dry.

Severe restrictions on residential and agri- cultural water use and a return to more normal rainfall patterns in the latter half of 2018 helped Cape Town postpone Day Zero, but the water situation there is still precari- ous. Residents are still limited to using 50 liters (13 gallons) of water per day, farms outside the city have had their irrigation supplies cut off, and long lines can still be found at natural springs and grocery stores when supplies of bottled water are deliv-

ered. Cape Town offers a cautionary tale of how even major cities can be at risk of water scar- city, especially as global climate change alters precipitation patterns and weather.

Dams in China and the United States One way to try to alleviate water scarcity and stress is through the construction of dams and water diversion projects. Dams are built across rivers to capture and store surface runoff in reservoirs. Dams can be utilized to control runoff to prevent floods, generate hydroelectric- ity, and supply water for agricultural, industrial, and residential uses. There are over 800,000 dams around the world, including close to 50,000 “large dams” that are 15 meters (50 feet) or higher. Combined, these dams capture and store close to 15% of global surface runoff for human uses. In the United States that figure is closer to 50%.

While dams can provide many benefits in terms of water supply and management, energy production, and recreation, they also have a number of problems associated with them. First, when rivers are dammed, they create reservoirs behind the dam that can displace entire com- munities. For example, China’s massive Three Gorges Dam (the largest in the world) displaced 1.2 million people and flooded 13 cities, 140 towns, and 1,350 villages. Second, dams can have dramatic impacts on native fish and wildlife species as well as alter important ecosystem functions and services that rivers provide. For example, a series of large dams on the Colorado River have fundamentally altered that ecosystem and reduced the flow of water from that river to the ocean to virtually a trickle.

Competing Water Use Along the Colorado The Colorado River also offers an example of a regional water system threatened by misman- agement, competing demands between users, and global climate change. The Colorado River originates on the western slopes of the Rocky Mountains in Colorado. From there it flows 2,400 kilometers (1,500 miles) to the Gulf of California in Mexico. Along the way, the Colorado River passes through mountain regions, deserts, and the Grand Canyon.

Bram Janssen/Associated Press Residents of Cape Town, South Africa, waiting in line for water. Water resources in Cape Town are at a premium, and restrictions are in place in response to severe water shortages.

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Section 5.3 Global Water Use and Demand

Almost 100 years ago, water managers in western states began a systematic process of building dams on the Colorado River and using massive water diversion systems to divide the river’s water between urban areas and agriculture. Today nearly 40 mil- lion people in cities such as Las Vegas, Phoe- nix, Los Angeles, and San Diego depend on water from the Colorado River, while over 70% of the water withdrawn is used to irri- gate 1.4 million hectares (3.5 million acres) of cropland that produces 15% of U.S. agri- cultural products.

Since at least 2000, however, warning signs have been flashing for Colorado River water managers and others in the region. Water levels in Lake Mead and Lake Powell (fed by the Colorado) have dropped dramatically, reveal- ing water lines like “bathtub rings” that show where the water level used to be. Decreasing winter snowfall totals in the Rocky Mountains, tied to global climate change, lead to reduced runoff and water supply in the summer months. Water shortages in the region are projected to get even worse with climate change, and water managers are already struggling to balance competing demands for water from urban and residential users versus agricultural users. Meanwhile, regional energy managers are making contingency plans for possible electricity shortages caused by declining hydroelectric production from the region’s dams.

Water Diversion and the Aral Sea An even more dramatic example of water misuse and mismanagement comes from central Asia. The Aral Sea, located on the border between Kazakhstan and Uzbekistan, was once the world’s fourth largest lake and roughly the size of the country of Ireland. Up until the 1960s the Aral Sea supported hundreds of lakeside communities, provided an estimated 60,000 jobs in the fishing industry, and provided important wildlife habitat and ecosystem services for the region (Bennett, 2008).

At the time, the region was part of the Soviet Union, and Soviet engineers and planners made the decision to divert water from two major rivers, the Syr Darya and the Amu Darya, that fed freshwater to the Aral Sea. The water was to be used for irrigation for cotton and wheat production. Dozens of large dams, almost 100 reservoirs, and over 30,000 kilometers (20,000 miles) of canals were constructed.

Gradually, the Aral Sea began to shrink in size, and by 2000 it split into a small northern por- tion and a larger southern portion. A few years after that, the southern portion split again into an eastern and western half. And in just the past few years, the southeastern portion has dried up completely. Overall, the Aral Sea has lost over 90% of the water it once contained. The former lakeside is littered with the rusted hulks of old fishing boats, and strong winds whip up dust storms that blow over former lakeside communities and sicken whatever resi- dents still remain.

Filippobnf/iStock /Getty Images Plus Damming of the Colorado River has drastically reduced the water level of Lake Mead. Here the former water level is indicated by the bathtub- like rings around the edges.

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