2Chapter Overview Questions Why is water so important, how much freshwater is available to us, and how much of it are we using?What causes freshwater shortages, and what can be done about this problem?What are the advantages and disadvantages of withdrawing groundwater?What are the advantages and disadvantages of using dams and reservoirs to supply more water?
3Chapter Overview Questions (cont’d) What are the advantages and disadvantages of transferring large amounts of water from one place to another?Can removing salt from seawater solve our water supply problems?How can we waste less water?How can we use the earth’s water more sustainably?What causes flooding, and what can we do about it?
4Updates OnlineThe latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at to access InfoTrac articles.InfoTrac: For money or for life. Jeff Conant. Earth Island Journal, Autumn 2006 v21 i3 p33(6).InfoTrac: Backstory: Tapping the world. The Christian Science Monitor March 22, 2006 p20.InfoTrac: A water crisis in the making. Christopher Meyer. Middle East Economic Digest, April 7, 2006 v50 i14 p47(2).Science Daily: Historic Colorado River Streamflows Reconstructed Back To 1490National Geographic: Map: Middle East Natural ResourcesScience Daily: Putting Coal Ash Back Into Mines A Viable Option For Disposal, But Risks Must Be Addressed
5Video: Western Drought This video clip is available in CNN Today Videos for Environmental Science, 2004, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.
6Core Case Study: Water Conflicts in the Middle East - A Preview of the Future Many countries in the Middle East, which has one of the world’s highest population growth rates, face water shortages.Figure 14-1
7Water Conflicts in the Middle East: A Preview of the Future Most water in this dry region comes from the Nile, Jordan or Tigris rivers.Countries are in disagreement as to who has water rights.Currently, there are no cooperative agreements for use of 158 of the world’s 263 water basins that are shared by two or more countries.
8WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Water keeps us alive, moderates climate, sculpts the land, removes and dilutes wastes and pollutants, and moves continually through the hydrologic cycle.Only about 0.02% of the earth’s water supply is available to us as liquid freshwater.
9WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Comparison of population sizes and shares of the world’s freshwater among the continents.Figure 14-2
10Percent of world's water resources and population Continent 36%Asia60.5%10%Africa14%8%Europe11.3%15%North and Central America7.3%Figure 14.2Natural capital shares: population and freshwater supplies on the world’s continents. QUESTION: What two major conclusions can you draw from these data? (Data from UNESCO, 2003)26%South America and Caribbean6.4%5%Oceania0.5%Fig. 14-2, p. 307
11WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Some precipitation infiltrates the ground and is stored in soil and rock (groundwater).Water that does not sink into the ground or evaporate into the air runs off (surface runoff) into bodies of water.The land from which the surface water drains into a body of water is called its watershed or drainage basin.
12Unconfined Aquifer Recharge Area Evaporation and transpiration PrecipitationEvaporation and transpirationEvaporationConfined Recharge AreaRunoffFlowing artesian wellRecharge Unconfined AquiferStream Well requiring a pumpFigure 14.3Natural capital: groundwater system. An unconfined aquifer is an aquifer with a permeable water table. A confined aquifer is bounded above and below by less permeable beds of rock where the water is confined under pressure. Some aquifers are replenished by precipitation; others are not.InfiltrationWater tableLakeInfiltrationUnconfined aquiferLess permeable material such as clayConfined aquiferConfining impermeable rock layerFig. 14-3, p. 308
13WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL We currently use more than half of the world’s reliable runoff of surface water and could be using 70-90% by 2025.About 70% of the water we withdraw from rivers, lakes, and aquifers is not returned to these sources.Irrigation is the biggest user of water (70%), followed by industries (20%) and cities and residences (10%).
14Water in the United States Average precipitation (top) in relation to water-deficit regions and their proximity to metropolitan areas (bottom).Figure 14-4
15Average annual precipitation (centimeters) Less than 4181–12241–81More than 122Figure 14.4Natural capital: average annual precipitation and major rivers (top) and water-deficit regions in the continental United States and their proximity to metropolitan areas having populations greater than 1 million (bottom). QUESTION: What is the water supply situation where you live or go to school? (Data from U.S. Water Resources Council and U.S. Geological Survey)Fig. 14-4a, p. 309
16Metropolitan regions with population greater than 1 million Figure 14.4Natural capital: average annual precipitation and major rivers (top) and water-deficit regions in the continental United States and their proximity to metropolitan areas having populations greater than 1 million (bottom). QUESTION: What is the water supply situation where you live or go to school? (Data from U.S. Water Resources Council and U.S. Geological Survey)Acute shortageShortageAdequate supplyMetropolitan regions with population greater than 1 millionFig. 14-4b, p. 309
17Case Study: Freshwater Resources in the United States 17 western states by 2025 could face intense conflict over scarce water needed for urban growth, irrigation, recreation and wildlife.Figure 14-5
18Highly likely conflict potential Substantial conflict potential Wash.MontanaN.D.OregonIdahoWyomingS.D.NevadaNeb.UtahKansasColo.CaliforniaOak.Figure 14.5Natural capital degradation: water hot spot areas in 17 western states that by 2025 could face intense conflicts over scarce water needed for urban growth, irrigation, recreation, and wildlife. Some analysts suggest that this is a map of places not to live over the next 25 years. QUESTION: Do you live or would you live in one of these hotspot areas? (Data from U.S. Department of the Interior)N.M.TexasHighly likely conflict potentialSubstantial conflict potentialModerate conflict potentialUnmet rural water needsFig. 14-5, p. 310
19TOO LITTLE FRESHWATERAbout 41% of the world’s population lives in river basins that do not have enough freshwater.Many parts of the world are experiencing:Rivers running dry.Lakes and seas shrinking.Falling water tables from overpumped aquifers.
20Stress on the World’s River Basins Comparison of the amount of water available with the amount used by humans.Figure 14-6
21Europe North America Asia Africa South America Australia Stress High Figure 14.6Natural capital degradation: stress on the world’s major river basins, based on a comparison of the amount of water available with the amount used by humans. QUESTION: What is the level of water stress where you live or go to school? (Data from World Commission on Water Use in the Twenty-First Century)StressHighNoneFig. 14-6, p. 311
22Case Study: Who Should Own and Manage Freshwater Resources There is controversy over whether water supplies should be owned and managed by governments or by private corporations.European-based water companies aim to control 70% of the U.S. water supply by buying up water companies and entering into agreements with cities to manage water supplies.
23How Would You Vote?To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment.Should private companies own or manage most of the world's water resources?a. No. Democratically elected governments, which are accountable to the voters, should own and manage water resources.b. Qualified yes. Governments should own the water, but expert private companies should manage it.c. Depends. Each case must be decided independently. The record on private versus public ownership is mixed.d. Yes. Private companies have more expertise and experience in managing water resources than most government bureaucrats.
24TOO LITTLE FRESHWATERCities are outbidding farmers for water supplies from rivers and aquifers.Countries are importing grain as a way to reduce their water use.More crops are being used to produce biofuels.Our water options are:Get more water from aquifers and rivers, desalinate ocean water, waste less water.
25WITHDRAWING GROUNDWATER TO INCREASE SUPPLIES Most aquifers are renewable resources unless water is removed faster than it is replenished or if they are contaminated.Groundwater depletion is a growing problem mostly from irrigation.At least one-fourth of the farms in India are being irrigated from overpumped aquifers.
26Withdrawing Groundwater Trade-OffsWithdrawing GroundwaterAdvantagesDisadvantagesUseful for drinking and irrigationAquifer depletion from overpumpingSinking of land (subsidence) from overpumpingAvailable year-roundExists almost everywherePolluted aquifers for decades or centuriesRenewable if not overpumped or contaminatedSaltwater intrusion into drinking water supplies near coastal areasFigure 14.7Trade-offs: advantages and disadvantages of withdrawing groundwater. QUESTION: Which two advantages and which two disadvantages do you think are the most important?No evaporation lossesReduced water flows into surface watersIncreased cost and contamination from deeper wellsCheaper to extract than most surface watersFig. 14-7, p. 313
27Groundwater Depletion: A Growing Problem Areas of greatest aquifer depletion from groundwater overdraft in the continental U.S.The Ogallala, the world’s largest aquifer, is most of the red area in the center (Midwest).Figure 14-8
28Groundwater Overdrafts: Figure 14.8Natural capital degradation: areas of greatest aquifer depletion from groundwater overdraft in the continental United States. Aquifer depletion is also high in Hawaii and Puerto Rico (not shown on map). QUESTION: Is groundwater depletion a problem where you live or go to school? (Data from U.S. Water Resources Council and U.S. Geological Survey)Groundwater Overdrafts:HighModerateMinor or noneFig. 14-8, p. 314
29Other Effects of Groundwater Overpumping Groundwater overpumping can cause land to sink, and contaminate freshwater aquifers near coastal areas with saltwater.Figure 14-11
30Fresh groundwater aquifer Major irrigation wellWell contaminated with saltwaterWater tableSea levelFresh groundwater aquiferSaltwaterFigure 14.11Natural capital degradation: saltwater intrusion along a coastal region. When the water table is lowered, the normal interface (dashed line) between fresh and saline groundwater moves inland, making groundwater drinking supplies unusable. QUESTION: What two things would you do to reduce the threat of saltwater intrusion?SeafloorInterfaceSaltwater intrusionInterfaceNormal interfaceFig , p. 315
31Other Effects of Groundwater Overpumping Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater.Figure 14-10
32Groundwater Pumping in Saudi Arabia (1986 – 2004) Irrigation systems from the nonrenewable aquifer appear as green dots. Brown dots are wells that have gone dry.Figure 14-9
33Groundwater Depletion SolutionsGroundwater DepletionPreventionControlWaste less waterRaise price of water to discourage wasteSubsidize water conservationBan new wells in aquifers near surface watersTax water pumped from wells near surface watersBuy and retire groundwater withdrawal rights in critical areasFigure 14.12Solutions: ways to prevent or slow groundwater depletion by using water more sustainably. QUESTION: Which two of these solutions do you think are the most important?Set and enforce minimum stream flow levelsDo not grow water-intensive crops in dry areasFig , p. 316
34USING DAMS AND RESERVOIRS TO SUPPLY MORE WATER Large dams and reservoirs can produce cheap electricity, reduce downstream flooding, and provide year-round water for irrigating cropland, but they also displace people and disrupt aquatic systems.
36Provides water for year-round irrigation of cropland Flooded land destroys forests or cropland and displaces peopleLarge losses of water through evaporationProvides water for drinkingDownstream cropland and estuaries are deprived of nutrient-rich siltReservoir is useful for recreation and fishingRisk of failure and devastating downstream floodingCan produce cheap electricity (hydropower)Figure 14.13Trade-offs: advantages (green) and disadvantages (orange) of large dams and reservoirs. The world’s 45,000 large dams (higher than 15 meters or 50 feet) capture and store 14% of the world’s runoff, provide water for almost half of all irrigated cropland, and supply more than half the electricity used by 65 countries. The United States has more than 70,000 large and small dams, capable of capturing and storing half of the country’s entire river flow. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Downstream flooding is reducedMigration and spawning of some fish are disruptedFig a, p. 317
37Powerlines Reservoir Dam Powerhouse Intake Turbine Fig. 14-13b, p. 317 Figure 14.13Trade-offs: advantages (green) and disadvantages (orange) of large dams and reservoirs. The world’s 45,000 large dams (higher than 15 meters or 50 feet) capture and store 14% of the world’s runoff, provide water for almost half of all irrigated cropland, and supply more than half the electricity used by 65 countries. The United States has more than 70,000 large and small dams, capable of capturing and storing half of the country’s entire river flow. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Fig b, p. 317
38Case Study: The Colorado Basin – an Overtapped Resource The Colorado River has so many dams and withdrawals that it often does not reach the ocean.14 major dams and reservoirs, and canals.Water is mostly used in desert area of the U.S.Provides electricity from hydroelectric plants for 30 million people (1/10th of the U.S. population).
39Case Study: The Colorado Basin – an Overtapped Resource Lake Powell, is the second largest reservoir in the U.S.It hosts one of the hydroelectric plants located on the Colorado River.Figure 14-15
40The Colorado River Basin The area drained by this basin is equal to more than one-twelfth of the land area of the lower 48 states.Figure 14-14
41UPPER BASIN LOWER BASIN Gulf of California IDAHOWYOMINGDamAqueduct or canalSalt Lake CityUpper BasinDenverLower BasinGrand JunctionUPPER BASINUTAHColorado RiverNEVADALake PowellCOLORADOGrand CanyonGlen Canyon DamLas VegasNEW MEXICOCALIFORNIABoulder CityLos AngelesARIZONAAlbuquerqueFigure 14.14Natural capital degradation: the Colorado River basin. The area drained by this basin is equal to more than one-twelfth of the land area of the lower 48 states. Two large reservoirs—Lake Mead behind the Hoover Dam and Lake Powell behind the Glen Canyon Dam (Figure 14-15)—store about 80% of the water in this basin.LOWER BASINPalm Springs100 mi.PhoenixSan DiegoYuma150 kmTucsonMexicaliAll-American CanalGulf of CaliforniaMEXICOFig , p. 318
42How Would You Vote?To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment.Do the advantages of large dams outweigh their disadvantages?a. No. Large dams inflict extensive environmental damage and humans must learn to meet their needs without them.b. Yes. Dams are critical in providing water and electricity for people, especially in developing countries.
43Case Study: China’s Three Gorges Dam There is a debate over whether the advantages of the world’s largest dam and reservoir will outweigh its disadvantages.The dam will be 2 kilometers long.The electric output will be that of 18 large coal-burning or nuclear power plants.It will facilitate ship travel reducing transportation costs.Dam will displace 1.2 million people.Dam is built over seismatic fault and already has small cracks.
44Dam RemovalSome dams are being removed for ecological reasons and because they have outlived their usefulness.In 1998 the U.S. Army Corps of Engineers announced that it would no longer build large dams and diversion projects in the U.S.The Federal Energy Regulatory Commission has approved the removal of nearly 500 dams.Removing dams can reestablish ecosystems, but can also re-release toxicants into the environment.
45TRANSFERRING WATER FROM ONE PLACE TO ANOTHER Transferring water can make unproductive areas more productive but can cause environmental harm.Promotes investment, jobs and strong economy.It encourages unsustainable use of water in areas water is not naturally supplied.
46Case Study: The California Experience A massive transfer of water from water-rich northern California to water-poor southern California is controversial.Figure 14-16
47Oroville Dam and Reservoir CALIFORNIANEVADAShasta LakeSacramento RiverUTAHOroville Dam and ReservoirFeather RiverNorth Bay AqueductLake TahoeSacramentoSan FranciscoHoover Dam and Reservoir (Lake Mead)South Bay AqueductFresnoSan Luis Dam and ReservoirSan Joaquin ValleyColorado RiverLos Angeles AqueductCalifornia AqueductARIZONAColorado River AqueductSanta BarbaraCentral Arizona ProjectFigure 14.16Solutions: California Water Project and the Central Arizona Project. These projects involve large-scale water transfers from one watershed to another. Arrows show the general direction of water flow. QUESTION: What two things would you do to improve this water transfer project?Los AngelesSalton SeaSan DiegoPhoenixTucsonMEXICOFig , p. 321
48Case Study: The Aral Sea Disaster The Aral Sea was once the world’s fourth largest freshwater lake.Figure 14-17
49Case Study: The Aral Sea Disaster Diverting water from the Aral Sea and its two feeder rivers mostly for irrigation has created a major ecological, economic, and health disaster.About 85% of the wetlands have been eliminated and roughly 50% of the local bird and mammal species have disappeared.Since 1961, the sea’s salinity has tripled and the water has dropped by 22 meters most likely causing 20 of the 24 native fish species to go extinct.
50DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIES Removing salt from seawater by current methods is expensive and produces large amounts of salty wastewater that must be disposed of safely.Distillation: heating saltwater until it evaporates, leaves behind water in solid form.Reverse osmosis: uses high pressure to force saltwater through a membrane filter.
51DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIES Seeding clouds with tiny particles of chemicals to increase rainfall towing icebergs or huge bags filled with freshwater to dry coastal areas have all been proposed but are unlikely to provide significant amounts of freshwater.
52INCREASING WATER SUPPLIES BY WASTING LESS WATER We waste about two-thirds of the water we use, but we could cut this waste to 15%.65-70% of the water people use throughout the world is lost through evaporation, leaks, and other losses.Water is underpriced through government subsidies.The lack of government subsidies for improving the efficiency of water use contributes to water waste.
53How Would You Vote?To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment.Should water prices be raised sharply to help reduce water waste?a. No. Poor people, farmers, ranchers, and small businesses would suffer from price increases.b. Yes. People would be more likely to conserve water if it is more expensive.
54INCREASING WATER SUPPLIES BY WASTING LESS WATER Sixty percent of the world’s irrigation water is currently wasted, but improved irrigation techniques could cut this waste to 5-20%.Center-pivot, low pressure sprinklers sprays water directly onto crop.It allows 80% of water to reach crop.Has reduced depletion of Ogallala aquifer in Texas High Plains by 30%.
55(efficiency 60% and 80% with surge valves) Drip irrigation(efficiency 90–95%)Gravity flow(efficiency 60% and 80% with surge valves)Figure 14.18Major irrigation systems: because of high initial costs, center-pivot irrigation and drip irrigation are not widely used. The development of new low-cost drip-irrigation systems may change this situation.Center pivot(efficiency 80%–95%)Water usually pumped from underground and sprayed from mobile boom with sprinklers.Above- or below-ground pipes or tubes deliver water to individual plant roots.Water usually comes from an aqueduct system or a nearby river.Fig , p. 325
56Reducing Irrigation Water Waste SolutionsReducing Irrigation Water Waste• Line canals bringing water to irrigation ditches• Level fields with lasers• Irrigate at night to reduce evaporation• Monitor soil moisture to add water only when necessary• Polyculture• Organic farmingFigure 14.19Solutions: methods for reducing water waste in irrigation. QUESTION: Which two of these solutions do you think are the most important?• Don't grow water-thirsty crops in dry areas• Grow water-efficient crops using drought resistant and salt-tolerant crop varieties• Irrigate with treated urban waste water• Import water-intensive crops and meatFig , p. 326
57Solutions: Getting More Water for Irrigation in Developing Countries – The Low-Tech Approach Many poor farmers in developing countries use low-tech methods to pump groundwater and make more efficient use of rainfall.Figure 14-20
58Solutions Reducing Water Waste • Redesign manufacturing processes • Repair leaking underground pipes• Landscape yards with plants that require little water• Use drip irrigation• Fix water leaks• Use water meters• Raise water prices• Use waterless composting toilets• Require water conservation in water-short citiesFigure 14.21Solutions: methods of reducing water waste in industries, homes, and businesses. QUESTION: Which three of these solutions do you think are the most important?• Use water-saving toilets, showerheads, and front loading clothes washers• Collect and reuse household water to irrigate lawns and nonedible plants• Purify and reuse water for houses, apartments, and office buildings• Don't waste energyFig , p. 327
59Raising the Price of Water: A Key to Water Conservation We can reduce water use and waste by raising the price of water while providing low lifeline rates for the poor.When Boulder, Colorado introduced water meters, water use per person dropped by 40%.A 10% increase in water prices cuts domestic water use by 3-7%.
60Solutions: Using Less Water to Remove Industrial and Household Wastes We can mimic the way nature deals with wastes instead of using large amounts of high-quality water to wash away and dilute industrial and animal wastes.Use nutrients in wastewater before treatment as soil fertilizer.Use waterless and odorless composting toilets that convert human fecal matter into a small amount of soil material.
61TOO MUCH WATERHeavy rainfall, rapid snowmelt, removal of vegetation, and destruction of wetlands cause flooding.Floodplains, which usually include highly productive wetlands, help provide natural flood and erosion control, maintain high water quality, and recharge groundwater.To minimize floods, rivers have been narrowed with levees and walls, and dammed to store water.
62TOO MUCH WATERComparison of St. Louis, Missouri under normal conditions (1988) and after severe flooding (1993).Figure 14-22
63TOO MUCH WATERHuman activities have contributed to flood deaths and damages.Figure 14-23
64Oxygen released by vegetation Forested HillsideOxygen released by vegetationDiverse ecological habitatEvapotranspirationTrees reduce soil erosion from heavy rain and windAgricultural landSteady river flowFigure 14.23Natural capital degradation: hillside before and after deforestation. Once a hillside has been deforested for timber and fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.”Leaf litter improves soil fertilityTree roots stabilize soil and aid water flowVegetation releases water slowly and reduces floodingFig a, p. 330
65Evapotranspiration decreases Roads destabilize hillsides After DeforestationTree plantationEvapotranspiration decreasesRoads destabilize hillsidesRanching accelerates soil erosion by water and windWinds remove fragile topsoilGullies and landslidesAgricultural land is flooded and silted upFigure 14.23Natural capital degradation: hillside before and after deforestation. Once a hillside has been deforested for timber and fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.”Heavy rain leaches nutrients from soil and erodes topsoilRapid runoff causes floodingSilt from erosion blocks rivers and reservoirs and causes flooding downstreamFig b, p. 330
66Preserve forests on watersheds SolutionsReducing Flood DamagePreventionControlPreserve forests on watershedsStrengthen and deepen streams (channelization)Preserve and restore wetlands in floodplainsBuild levees or floodwalls along streamsTax all development on floodplainsFigure 14.24Solutions: methods for reducing the harmful effects of flooding. QUESTION: Which two of these solutions do you think are the most important?Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry, and recreationBuild damsFig , p. 331
67SOLUTIONS: USING WATER MORE SUSTAINABLY We can use water more sustainably by cutting waste, raising water prices, preserving forests and wetlands in water basins, and slowing population growth.Figure 14-25
68What Can You Do? Water Use and Waste • Use water-saving toilets, showerheads, and faucet aerators.• Shower instead of taking baths, and take short showers.• Stop water leaks.• Turn off sink faucets while brushing teeth, shaving, or washing.• Flush toilets only when necessary.• Wash only full loads of clothes or use the lowest water-level for smaller loads.• Use recycled (gray) water for lawn, gardens, house plants, car washing.• Wash a car from a bucket of soapy water, and use the hose for rinsing only.Figure 14.25Individuals matter: ways you can reduce your use and waste of water. Visit for an array of water-saving tips from the EPA and the California Urban Water Conservation Council that can be used anywhere. QUESTION: Which four of these actions do you think are the most important?• If you use a commercial car wash, try to find one that recycles its water.• Replace your lawn with native plants that need little if any watering and decorative gravel or rocks.• Water lawns and gardens in the early morning or evening.• Sweep or blow off driveways instead of hosing off with water.• Use drip irrigation and mulch for gardens and flowerbeds.Fig , p. 333