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3 Water for the Future Decisions about investments in desalination technologies should be made in a comprehensive and consistent manner that adequately consid- ers a wide range of economic, environmental, and political factors. Among the most important factors are how future demands for water are to be evaluated or forecasted, and how those projected demands are to be satisfied given a wide range of water supply alternatives. The past few years have seen a growing interest in, and worry about, the issue of water scarcity in arid and semi-arid regions of the United States. That concern has now spread to the more humid regions of the country, and the avail- ability of water to satisfy growing demands for domestic, agricultural, and environmental uses is now a matter of increasing concern in virtually all regions. This chapter assesses the various forces and factors affecting supply and demand for water and emphasizes the ways in which those factors may affect the social attractiveness and economic competitive- ness of desalination technologies. Examples of the need to reevaluate water supply and demand abound. The City of Atlanta is struggling to find supplies to support its rapidly expanding urban areas, while Florida is concerned about using the same watersheds to maintain adequate flows to protect ecosystems and wetlands. The states of Maryland and Virginia needed the Supreme Court to help them resolve a dispute about use of the shared waters of the Potomac River (Virginia v. Maryland, 540 U.S. 129 ). The alloca- tion of the waters of the Missouri River basin between navigational pur- poses in support of agriculture on the northern plains and environmental uses, including support for a number of endangered species, is the sub- ject of continuing and unresolved controversy (NRC, 2002b). Colorado River water management continues to be a focus of dispute among seven western states and Mexico (NRC, 2007). And perennial water problems in California have been heightened by a recent court decision that may reduce water pumping for agricultural and urban uses to protect the en- dangered delta smelt (Ricci and Bailey, 2007). 38
Water for the Future 39 As population and regional economies grow in the future and as the importance of providing water to support environmental services be- comes more widely appreciated, the overall pressure on the nationâs lim- ited water resources will continue to intensify. Simultaneously, interest in finding novel means of managing these pressures will also intensify as the limitations of traditional infrastructure solutions are becoming better understood. In recent years, increased attention has been drawn to the promise and prospects of desalination technology for alleviating the growing wa- ter scarcity. At its simplest, the technology might substantially reduce water scarcity by making the almost inexhaustible stock of seawater and the large quantities of brackish groundwater that appear to be available into new sources of freshwater supply. Historically, the deployment and use of desalination technology has been constrained because of its high costs, and its use has been confined to places in the world where energy is cheap and alternative sources of supply are either unavailable or espe- cially costly. However, recent advances in technology, especially im- provements in membranes that can be used in desalinating both brackish water and seawater, have rekindled more widespread interest in desalina- tion. Indeed, the total costs of desalinating brackish water and seawater (including concentrate management costs) in the United States may now be competitive with other alternatives in some locations and for some high-valued uses, fueling optimism over the prospects for the expanded use of desalination technology. Seawater desalination technology is unique among supply augmenta- tion alternatives in that it is not dependent on the hydrological cycle and can produce water as reliably during drought events as at other times. Brackish groundwater desalination can also provide reliable water sup- plies during short-term droughts, although longer periods of drought can affect regional groundwater availability. The recent occurrence of severe droughts in many areas of the country and the prediction that global cli- mate change will likely result in regional increases in the frequency and intensity of extreme events have heightened public sensitivity to the vari- ability of the hydrologic cycle. Consequently, desalination technology is attractive both because it offers the possibility of supplying large amounts of new water and because it can do so reliably. There is consid- erable interest, therefore, in advancing desalination technology and con- centrate management alternatives and hastening the time when the costs are routinely competitive with the costs of other alternatives. At the same time, too heavy a reliance on any one source of water also imposes risks and vulnerabilities. This chapter reviews historical and current thinking about the con- cept of water availability, use, scarcity, and sufficiency. Trends in U.S. and regional water use are presented along with a review of experience
40 Desalination: A National Perspective with water demand forecasts. The role of water planning and projections is also discussed in the context of assisting decisions about long-term investment in technologies such as desalination and nontechnological solutions such as demand management and water efficiency improve- ments. ELEMENTS OF WATER SUFFICIENCY During the nineteenth and twentieth centuries, the demand for water rose dramatically with growing populations and economies. Billions of dollars were spent on thousands of large water projects designed to con- trol floods, move water vast distances, disinfect and treat water supplies, and deliver water for irrigation or hydropower. Even today, worldwide, tens of billions of dollars are spent annually on new dams (World Com- mission on Dams, 2000). Today, many of the largest cities of the United States rely on water brought from hundreds and even thousands of kilo- meters away. Agricultural productivity is highest where irrigation miti- gates the effects of climatic variability, such as in Californiaâs Central Valley. The growing discussion about expanding investments in desali- nation technology reflects the perception that demands for water are growing in places where natural availability is constrained by environ- mental, financial, or social factors. In recent years, however, a shift away from the construction of new water infrastructure and toward rethinking the active management of wa- ter use has started to occur, in part because of the improved understand- ing of the true financial, social, and environmental costs of large infra- structure, and in part as a result of new thinking about how best to meet the water requirements of human needs and desires (e.g., Douglas et al., 1998; Gleick, 2003a). New water facilities are still needed in many parts of the world, and the existing infrastructure must be maintained in order to keep the flow of benefits coming. But water planners and managers, as well as those responsible for using and paying for water, are now begin- ning to evaluate the other side of the equationâhow society uses and manages water. People require modest amounts of water for drinking, cooking, cleaning, and hygiene to maintain human well-being. For certain re- quirements, the actual âdemandâ for water may be unrelated to the minimum amount of water âneededâ for that required benefit. Water de- mand to flush a toilet can range from 23 liters (6 gallons) in an old, inef- ficient U.S. toilet, to 5 liters (1.6 gallons) in a model that meets current U.S. standards, to zero liters in an efficient electric or composting toilet. New digital photography provides a faster, more detailed image while completely eliminating the water used by old film processing. In these
Water for the Future 41 examples, what is actually being demanded is not a specific amount of water but reliable services of removing wastes or producing goods and services (Gleick, 2003a). In addition, as income grows, people want rec- reation, leisure, and luxury goods. Providing these needs and wants can be accomplished in many ways that depend on technology, prices, cul- tural traditions, and other factors, often with radically different implica- tions for water. Increasingly, water providers are exploring ways to de- liver diverse water services matched to the usersâ needs and are working with water users at local and community scales. These changes in water policy, planning, and management have resulted in a dramatic change in the relationship between water withdrawals and population growth. Review of U.S. Water Use over Time Beginning in 1951, the U.S. Geological Survey (USGS) has pub- lished a series of comprehensive reports on water use in the United States at approximately 5-year intervals (e.g., Hutson et al., 2003; MacKichan, 1951, 1957; MacKichan and Kammerer, 1961; Solley et al., 1998). These assessments include estimates of surface and groundwater use separated into various water-use categories for all 50 states and by major hydro- logic regions. (Definitions of âuseâ vary across studies and common ver- nacular; therefore, some standard definitions are provided in Box 3-1.) The initial study in this series estimated water use for all withdrawals, including municipal, rural, domestic, livestock, irrigation, industrial, and hydroelectric power. Water for in-stream flows such as navigation, rec- reation, and fish and wildlife were also addressed, though only qualita- tively. Consumptive use of water began to be estimated in the 1960 re- port, and estimates were made of water use in the early decades of the century, beginning in 1900 (CEQ, 1991; MacKichan, 1957; NRC, 2002a). The most recent report, however, has eliminated several catego- ries of information on water use. Consumptive use, in particular, is no longer reported, which will make tracking some of the most important impacts more difficult. There are significant differences in the depth and quality of water- use data because of differences in types of water use, methods of data collection, reliability of reporting, and funding priorities (DOI, 2002). As a result, the National Research Council (NRC, 2002a) recommended a series of improvements in the U.S. National Water-Use Information Pro- gram to help provide more comprehensive and accurate water-use data in the future (see Box 3-2).
42 Desalination: A National Perspective BOX 3-1 Definitions of Water Use, Conservation, and Efficiency Terms There is confusion in the water literature about the terms use, need, with- drawal, demand, consumption, and consumptive use of water. The term water use, while common, can mean many different things, referring at times to con- sumptive use and at times to withdrawals of water. Withdrawal usually refers to water removed from a source and used to meet a human need. Some of this water may be returned to the original source with changes in the quantity and quality of the water, but some may be used consumptively. The term consump- tive use or consumption typically refers to water withdrawn from a source and made unavailable for reuse in the same basin, such as through conversion to steam, losses to evaporation or transpiration, seepage to a saline sink, or con- tamination. Consumptive use is sometimes referred to as irretrievable or irrecov- erable loss. Thermoelectric power plants typically withdraw substantial amounts of water for cooling but consume little, returning that water directly to the river, albeit warmer, for use by the next downstream user. A farmer may withdraw large amounts of water for irrigation, but the vast majority of it may be used con- sumptively by plants and be lost to any downstream users. Need for water is also a subjective term, but it usually refers to the minimum amount of water required to satisfy a particular purpose or requirement. The term need implies, usually incorrectly, that water is required to satisfy a purpose without regard to price. Thus, the term also sometimes refers to the desire for water on the part of a wa- ter user. Demand for water is an economic concept that is used to describe a want for water backed up by a willingness to pay. A demand schedule or curve (the graphical representation of demand as a function of price) summarizes the quantities and qualities of water that consumers are willing to take at different prices. Demand curves almost invariably show that the higher the price, the lower the quantity taken, though the slope of the curve varies with many factors (Boland et al., 1984). Despite limitations in the data, these water-use studies have proven to be extremely valuable for both researchers and policy makers. One of the most important findings from the long-term data has been an unex- pected change in the trend of U.S. water use. Both total U.S. freshwater withdrawals and gross national product exhibited rapid growth until the late 1970s (Figure 3-1). Although economic growth continued to rise exponentially, water withdrawals began to level off and even decline, a change not noted or recognized by water managers or policy makers until the 1990s. This decline, however, has persisted; indeed, it is even more apparent when per-capita use is measured (Figure 3-2). Since the late 1970s, per-capita withdrawals have declined nearly 25 percent and now are at levels comparable to those of the late 1950s and early 1960s. Yet U.S. population has grown from approximately 180 million in 1960 to over 300 million in 2006 (U.S. Census Bureau, 2007). While no detailed analysis of the reason for these trends has been prepared, two major factors are relevant: changes in the efficiency of
Water for the Future 43 BOX 3-2 Challenges to Reporting Water Use Data Despite the value of consistent national water-use data and recommenda- tions from the National Research Council for improvements in data collection (NRC, 2002a), recent cutbacks imperil the development of effective national wa- ter policy. The most recent USGS national water-use report (Hutson et al., 2003; based on data from 2000), for example, cut back on collection and presentation of data for several categories of use, including mining, livestock, and aquacul- ture. Data were only compiled for states where water uses in these categories are large. Withdrawals from major groundwater aquifers are only being reported for public supply, irrigation, and industry. Data on commercial water use, waste- water treatment, reservoir evaporation, and hydroelectric power are no longer being collected, nor is information on consumptive use, reclaimed wastewater, return flows, or deliveries from public suppliers. Researchers and water planners depend on many of these data to understand long-term trends in sectoral and regional water use 700 $10,000 $9,000 600 Total US Water $8,000 Withdrawals Cubic kilometers per year 500 $7,000 Billion 1996 dollars $6,000 400 $5,000 300 US GNP $4,000 200 $3,000 $2,000 100 $1,000 0 $0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year FIGURE 3-1. Gross national product (GNP, in billions of 1996 dollars) and total water withdrawals (cubic kilometers per year). Water withdrawal data from MacKichan (1951, 1957), MacKichan and Kammerer (1961), Solley et al. (1998), and Hutson et al. (2003). Economic data from Johnston and Williamson (2002). Data on water withdrawals before 1950 come from CEQ (1991).
44 Desalination: A National Perspective 700 300 600 250 Cubic kilometers per year 500 Millions of people 200 400 Population of US 150 300 100 200 Total US Water Withdrawals 50 100 0 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year FIGURE 3-2. Total freshwater withdrawals in the United States from 1900 to 2000 (in cubic kilometers per year). Total water withdrawals based on data from MacKichan (1951, 1957), MacKichan and Kammerer (1961), CEQ (1991), Solley et al. (1998), and Hutson et al. (2003). Population based on data from U.S. Cen- sus Bureau (2001). water use and changes in the structure of the U.S. economy (Gleick, 2003b). In the first case, significant improvements in technology have led to reductions in the amount of water required to produce specific goods and services. For example, new national appliance standards put in place in the mid-1990s have reduced the amount of water required to flush a toilet from an average of 6 gallons per flush to 1.6 gallons per flush. Similar standards have reduced flow rates of showerheads. Other factors have also played a role. Producing a ton of steel before World War II required 100 to 200 tons of water (Kollar and MacAuley, 1980; National Association of Manufacturers, 1950). By the turn of the millen- nium, competitive economic pressures and water quality discharge regu- lations had driven improvements in water-use efficiency in the best steel plants to less than 4 tons of water per ton of steel (Posco Steel, 2007). Changes in design and production processes also play a role: a ton of aluminum can be produced using only one and a half tons of water. Thus, as automobile production replaces steel with aluminum, as has been hap- pening for many years, total water use per unit car drops further (Gleick, 2002). Some differences in water-use trends can be seen in an analysis of water use in various sectors. Although overall water use in the United
Water for the Future 45 States has remained roughly the same over the past 30 years, per-capita water use has decreased substantially (see Figures 3-1 and 3-2). Most of the magnitude of this decline comes from reductions in water withdraw- als for irrigation, power plant cooling, and other industrial uses. There have been modest and regular increases in public water supply with- drawals in the United States, primarily for residential use, increasing ap- proximately 2 million m3/day per year (see Figure 3-3). Most reductions in agricultural water use have come about because of improvements in irrigation technology, including precision irrigation and better monitor- ing of soil moisture, both of which can reduce water use and increase the reliability and yield of crop production. Changes in the nature of economies have played a role in reducing industrial water use (Figure 3-3). In the United States, the economy is less dependent on water-intensive industries such as mining, milling, and manufacturing and more a function of sectors that require less water per unit of output, such as telecommunications, computers, and services. De- creases in industrial water use are also the result of national legislation that set standards for the quality of wastewater discharges. One of the least expensive ways of meeting the federal water quality standards is to reduce the overall volume of water used, which led many industries to seek changes to the way process water was used. Reductions in water withdrawals for thermoelectric power produc- tion have been driven by the gradual replacement of once-through cool- ing systems with systems that recycle water (Figure 3-3). This trend will 700 Total withdrawals Public supply 600 Thermoelectric power use Other industrial use Irrigation Cubic kilometers per year 500 Livestock, aquaculture 400 300 200 100 - 0 1950 1960 1970 1980 1990 2000 Year FIGURE 3-3. Changes in U.S. water withdrawals by sector. Data from MacKi- chan (1951, 1957), MacKichan and Kammerer (1961), Solley et al. (1998), and Hutson et al. (2003).
46 Desalination: A National Perspective accelerate in the future as the Environmental Protection Agency requires more once-through cooling to be phased out (Clean Water Act Section 316b; see Box 5-1). Details on changes in regional water use are also available from in- dividual state data and from the USGS. As an example, Figure 3-4 shows long-term water withdrawals for California (1960 to 2000). In parallel with national trends, California has experienced substantial growth in population and economic indicators but declining per-capita water with- drawals (Hutson et al., 2003; MacKichan, 1951, 1957; MacKichan and Kammerer, 1961; Solley et al., 1998). Total water withdrawals in Cali- fornia have declined from a peak in 1980 and have remained roughly level since the mid-1980s, with an upward trend in water withdrawals in recent years. As with the rest of the United States, California irrigation withdrawals have dropped since 1980, and total urban water use has grown modestly since 1960 (Figure 3-4). Similarly, total water use in Texas has held relatively steady for over 25 years, although municipal water use increased steadily between 1974 and 2000 (Figure 3-5). In con- trast, the City of Seattle has substantially reduced total water use since the late 1960s (see Figure 3-6) despite a 40 percent increase in popula- tion through comprehensive and consistent water efficiency programs (Seattle Public Utilities, 2007). 180 Total Use 160 Million cubic meters per day 140 120 Agricultural Use 100 80 60 Urban and Domestic 40 Use 20 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Year FIGURE 3-4. Water withdrawals in the state of California. SOURCES: Data from MacKichan (1951, 1957), MacKichan and Kammerer (1961), Solley et al. (1998), and Hutson et al. (2003).
Water for the Future 47 70 Total Agricultural Municipal 60 Industrial/Mining Million cubic meters per day 50 40 30 20 10 0 1970 1975 1980 1985 1990 1995 2000 2005 Year FIGURE 3-5. Texas water use, including both groundwater and surface water, between 1974 and 2004. SOURCE: Data from Texas Water Development Board (2007). 0.7 1,400,000 Million cubic meters per day 0.6 1,200,000 Water Use 0.5 1,000,000 Population Population 0.4 800,000 0.3 600,000 0.2 400,000 0.1 200,000 0.0 0 1930 1950 1970 1990 2010 Year FIGURE 3-6. Water use in the city of Seattle. SOURCE: Data from Seattle Public Utilities (2007).
48 Desalination: A National Perspective These trends in water demand have important implications for water planners, infrastructure development, and water policy. In particular, the traditional assumption by planners that economic and population growth lead to growth in total water withdrawals and necessary expansion of supply now appears to be incorrect or, at least, not inevitable. These changing trends also support the idea that improvements in water-use efficiency and shifts in economic structure can reduce resource use, even in an expanding economy (Gleick, 2003a), considering the ability to shift and reallocate water uses through the development of water markets, trades, or changes in water rights. Future demands for water, however, may begin to rise again, and some regions of the United States may show far different trends for water use than the national average. For example, the growing emphasis on the production of biofuels is encouraging a shift to irrigation, even in regions like the Southeast where irrigation has not traditionally been used. Re- gional differences in water use are the result of variations in population dynamics, levels of effort to identify and reduce inefficiencies in water use, local water management practices, and other factors. Review of U.S. Water Quality Challenges Water quality is defined in response to variable concentrations of tens of thousands of natural and anthropogenic compounds, biologic ma- terial, many natural stable and radioactive elements, color, odor, and temperature. Even if an abundant quantity of water exists in a geographic region, water supply shortages may occur if the water quality is ill-suited to the specific societal demands. Water suitable for transportation of grain barges, cooling, or hydroelectric generation may not be appropriate for manufacture of semiconductor chips, public drinking supply, irriga- tion, or ecological uses. In addition, health studies are identifying new contaminants of concern, including methyl tertiary butyl ether (MTBE), perchlorate, pharmaceuticals, and more (NRC, 1996, 1999, 2005). Wa- ter-quality criteria (e.g., Safe Drinking Water Act amendments of 1996) are also evolving with time in response to epidemiological studies and technological advancements in analytical techniques and instrumentation that identify new environmental impacts and the presence of lower con- centrations of solutes and biologic materials. As large portions of the accessible nonsaline waters in the United States are fully allocated, some regions have little existing high-quality water available for expanding water supplies without negatively affecting environmental resources or other previously allocated water resources. Thus, water managers are increasingly turning to existing lower-quality water supplies, such as municipal and industrial wastewater, urban storm
Water for the Future 49 runoff, and saline water, such as seawater or brackish groundwater, to address new demands. Meanwhile, some existing water sources are fac- ing increasing water-quality degradation due to nonpoint sources of pol- lution from land use and development, agricultural chemicals, and other practices (Kolpin et al., 1995; Snyder et al., 2000). Society has developed a wide range of engineering techniques and methods to modify water quality for specific uses. Desalination, for example, removes salts to permit the use of saline water sources for drinking water, irrigation, or industrial uses and has the ability to provide a very specific, tailored wa- ter quality from quite different source qualities. The wider use of mem- brane desalination technology may have the side benefit of helping to remove some emerging contaminants that otherwise are not removed by conventional treatment (Synder et al., 2007). Water Use Projections for the Future Designing and building major water infrastructure is time and capital intensive. As a result, water planners traditionally take a relatively long view by making projections of future demands. These projections pro- duce expectations about future water use that in turn drive financial ex- penditures for water supply projects. Overestimates of supply needs can lead to unnecessary investment, environmental damage, and social and political risk. Underestimates of supply needs can lead to the failure to make timely investments, water supply shortages, and a reduction in sys- tem reliability. Water planners must balance these risks and benefits. How can future water demands be predicted, given the uncertainties involved in looking into the future? Many projections of future U.S. wa- ter demands have been made over the past half-century (Brown, 1999; Thompson et al., 1971; USDA and USFS, 1989; U.S. Senate Select Committee on National Water Resources, 1961; Viessman, 1980; Woll- man and Bonem, 1971; WRC, 1968, 1978). Review of the major studies that have been done reveals two noteworthy trends: overestimating total future water demand at the national level, often substantially, is the norm, not the exception; and, as tools and methods for making forecasts have improved, forecasts of future water needs have dropped (Gleick, 2003a). Figure 3-7 shows more than 15 different U.S. water projections made before 2005 together with actual water withdrawals. As the figure shows, every projection made before 1995 substantially overestimated future water demands by assuming that use would continue to grow at, or even above, historical growth rates. The earliest projections routinely overes- timated water demands because of their dependence on relatively simple assumptions about the relationship between water use, population, and
50 Desalination: A National Perspective FIGURE 3-7. Projections of total U.S. water withdrawals since the 1960s. The points indicate projected withdrawals; the colored lines lead back to the date the projection was made. SOURCES: Water withdrawal data from MacKichan (1951, 1957), MacKichan and Kammerer (1961), Solley et al. (1998), and Hutson et al. (2003). Forecast data from Wollman and Bonem (1971), U.S. Senate Select Committee on National Water Resources (1961), WRC (1968, 1978), Viessman (1980), NWC (1971), USDA and USFS (1989), and Brown (1999). industrial, commercial, and residential end-use intensity (e.g., water use per unit population, employment, revenue, or income). Agricultural wa- ter-use projections typically adopted constant end-use factors such as water per acre, which failed to incorporate either changes in water-use intensity of irrigation method, or changing cropping patterns. Most sce- narios ignored water requirements for in-stream ecological needs, navi- gation, hydropower production, and recreation. And almost all of these forecasts showed dramatic increases in demand over time, sometimes to implausible levels of future use that led many observers to worry about water shortfalls and shortages. This history suggests that the traditional methods used by water-scenario developers are missing some critically important real-world dynamics (Gleick, 2003a). Large-scale water-use projections have become increasingly sophis- ticated due to the growing capability of easily accessible computers to handle significant calculations and the growing availability of water-use data. Assessments that were conducted for continental areas or on a na- tional basis are now being performed for watersheds on smaller and smaller temporal and spatial scales (Alcamo et al., 1997; Gleick, 1997).
Water for the Future 51 The methods and tools used for forecasting and scenario analysis continue to rely heavily on traditional methods for making projections, but examples are emerging of new tools and new assumptions being used as planners reevaluate the driving factors behind changes in demands for water. Figure 3-8, for example, shows projections for Tampa Bay, Flor- ida. This figure shows modest improvements in efficiency over time, but it still relies heavily on the assumption that per-capita water use will re- main relatively unchanged while population grows into the future. Figure 3-9, however, shows forecasts produced by the City of Seattle, which has implemented a wide range of water management strategies to reduce sec- toral and per-capita demand. As a result, Seattleâs official water demand forecast now projects flat or declining water use through 2030 and small increases beyond that. Similarly, the State of California prepares a new water plan every 5 years, and the most recent version incorporates new estimates of significant water-use efficiency potential and evaluations of multiple scenarios. Even in the âcurrent trendsâ scenario, the entire state is projected to use less water in 2030 than it uses at present, largely be- cause of improvements in urban and agricultural water-use efficiency and changing land-use patterns (California Department of Water Re- sources, 2005). 1,000,000 900,000 Projected Demand Actual and projected water demand (m /d) 3 800,000 Actual Demand 700,000 600,000 500,000 400,000 300,000 200,000 100,000 0 18 19 20 21 22 23 24 25 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 97 98 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 19 19 19 Year FIGURE 3-8. Actual and forecasted water demand for Tampa Bay, Florida. SOURCE: Jerry Maxwell, Tampa Bay Water, personal communication, 2007.
52 Desalination: A National Perspective 0.7 Current Firm Yield 0.6 2004 Forecast Million cubic meters per day Actual 0.5 Demand 2007 Forecast 0.4 The gray area represents the added uncertainty involved in 0.3 extrapolating beyond 2030. 0.2 0.1 0 95 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 2055 2060 FIGURE 3-9. Actual demand, 2004 demand forecast, the most recent 2006 de- mand forecast, and estimated firm yield of water supply in the Seattle region. Note that the most recent demand forecast is well below the 2004 forecast, be- low average past demand through 2030, and remains below the firm yield of pre- sent supply through 2060. SOURCE: Bruce Flory, Seattle Public Utilities, personal communication, 2008. Although recent national water demand projections show relatively little increase in total water demand with time (Brown, 1999), some re- gions may show notably different trends than the national average. As mentioned previously, these regional differences result from variations in population growth, levels of effort to identify and reduce inefficiencies in water use, local water management practices, and other factors. Also, some regions may choose to reduce withdrawals from existing water supply sources for environmental reasons, thereby increasing the need for additional water sources while the total human demand remains un- changed (see Box 3-3). OPTIONS FOR MAINTAINING WATER SUFFICIENCY The definition of what is and is not a sufficient quantity and quality of water for a given purpose will vary with population, economic devel- opment, indigenous supplies of water, water quality considerations, and other factors. Perhaps the most significant feature of this concept is that it emphasizes the fact that past patterns of water use and past levels of
Water for the Future 53 BOX 3-3 Desalination for Environmental Uses While most of the discussion of desalination has focused on producing new water to supplement human uses, there is growing interest in the possibility of building desalination facilities that also directly or indirectly serve environmental needs. In some regions, human use of water has led to serious degradation of water quality and ecosystem habitat in rivers and streams. Efforts to restore that habitat rely, in part, on the ability of humans to reduce consumptive uses of water in order to return minimum flows to watersheds. In this context, some proposed desalination facilities could serve to replace, rather than supplement, existing sources of supply. For example, the California State Water Resources Control Board (SWRCB) ordered a reduction in diversions of water from the Carmel River in central California because of impacts on local threatened fish popula- tions. The order (SWRCB, 1995) requires that any new supplies produced by the local water provider be used on a one-to-one basis to offset these diversions. One option under consideration is the construction of a desalination plant that would serve to satisfy the SWRCB order (Cooley et al., 2006). sufficiency are not necessarily a guide to optimum patterns and levels of water use in the future. This comports with economic notions of supply and demand where the equilibrium quantities of water (and prices) are determined by the interaction of supply and demand. Inasmuch as the variables that affect supply and demand change over time, those equilib- rium quantities (and prices) will change in response. The most desirable quantities and prices for water supply are not al- ways strictly determined by the elements of economic supply and de- mand, although those elements will always be important determinants of water sufficiency. Departures from strict supply and demand solutions may be caused by (1) the presence of technical external diseconomies;1 (2) the public good attributes of some water services; (3) capital inten- sive industries such as airlines, natural gas, and water supply, where the dominance of capital or fixed costs prevents pricing the output according to its marginal cost; and (4) equity and welfare considerations. Despite the presence of one or more of these factors, the elements of supply and demand provide a useful framework for analyzing the various options available to maintain water sufficiency. 1 External diseconomies are said to occur when some of the costs of an eco- nomic transaction fall on persons who were not parties to the transaction. Thus, for example, you may purchase an automobile. If in the manufacturing of that vehicle, some of the wastes of production are discharged into a river, then the manufacturer is externalizing the costs of waste disposal on people who use the river for recreation by degrading its quality. The recreational users are third par- ties to the decision to produce and sell the automobile and yet they are made to bear some of the costs. They are said to have borne the external diseconomies.
54 Desalination: A National Perspective Historically, strategies for developing and managing water have tended to focus on supply-side options. These include the construction of storage and conveyance facilities that allow water to be captured and stored at wet times and places and transported for use at dry times and places. Most of the economical and environmentally acceptable surface- water storage opportunities in the United States have already been devel- oped, and interest in storage has now shifted to the many opportunities for underground storage of water and the conjunctive or joint manage- ment of surface and groundwater. In addition, attention has tended to shift toward new forms of supply that convert previously unusable or unused sources of water into useful resources, such as wastewater recla- mation and the desalination of brackish water and seawater. Although such technologies have tended to be very expensive, a combination of declining process costs and intensifying water scarcity is making them attractive options in some circumstances. In recent decades, as supply options have become more constrained and expensive, attention has also been focused on demand management options. These options, which focus on tools to help reduce the amounts of water required to satisfy any given need, include (1) water metering and monitoring to inform people about actual water-use patterns, (2) education about the costs and benefits of water efficiency technologies and strategies, (3) pricing as a tool for encouraging efficient use and sig- naling consumers about the true costs of providing water, (4) water-use regulations and norms that encourage or require the use of xeriscaping and other efficiency technologies, (5) the elimination of subsidies that encourage inefficient water use or planting of low-valued, high-water- using agricultural crops, and (6) the development and adoption of water- saving irrigation technology and on-farm water-management practices. There are also institutional options for addressing water scarcity, such as approaches for changing water allocations and rights. In some circumstances, water needed to sustain population and economic growth can be most economically obtained by reallocating water from relatively low-valued uses to higher-valued uses. This can be done through water markets or market-like mechanisms in which water can be exchanged, sold, or leased. Such market-like reallocations have been made recently from the Imperial Irrigation District in southeastern California and the San Diego County Water Authority. Other examples abound throughout the western United States (MacDonnell, 1990). These arrangements tend to be attractive in circumstances where the costs of supplementary sup- plies are relatively high and there are low-valued uses that make little sense to serve if higher-valued uses would otherwise go begging. Water scarcity in some regions of the United States will certainly in- tensify over the coming decades. No one option or set of options is likely to be sufficient to manage this intensifying scarcity. Rather, the most
Water for the Future 55 successful management strategies will be developed by considering all of the available alternatives and emphasizing the development of those best adapted economically, technically, politically, and socially to the circum- stances at hand. This comprehensive approach, sometimes called the âsoft path,â also acknowledges that different components of supply and demand management may differ in terms of the quality of the water, the cost of the water, and the reliability with which it is available (Gleick, 2002). When different tools are put together to meet particular manage- ment challenges, it is sometimes termed the âportfolio approachâ (see Box 3-4). BOX 3-4 Use of the Portfolio Approach to Water Management in San Diego County The experience of the San Diego County Water Authority, a wholesaler of water, illustrates the use of multiple water-management approaches to address water demand. In 1991, the agency imported 95 percent of its supply through the Metropolitan Water District of Southern California. The remaining 5 percent came from local surface-water sources. Since that time, the San Diego County Water Authority has pursued a strategy of developing a broader portfolio of tools, diver- sifying its sources of supply, maximizing the efficient use of existing resources, and reducing its demands on imported supplies. Imported supplies tend to be vulnerable to large earthquakes and subject to other sources of uncertainty such as drought and legal disputes over water rights and water allocations. By 2005 the component of supply imported from the Metropolitan Water District accounted for only 79 percent of the total (see Figure 3-10). Conservation, the development and use of recycled water, an increase in the quantity of surface water supply, the development of some local groundwater, and water acquired via a market- like transfer from the Imperial Irrigation District were added to the portfolio. Groundwater, 2% IID Transfer, 4% Local Surface Water, 7% Recycled Water, 2% Conservation, 7% MWD Transfer, 78% FIGURE 3-10: Water supply portfolio for San Diego in the year 2005. SOURCE: Robert Yamada, San Diego County Water Authority, personal communication, 2006. continued
56 Desalination: A National Perspective As the population of the Authorityâs service area continues to grow, water availability will also have to grow if the new population is to be served. The San Diego County Water Authority estimates that it will need to increase supply by 185,022,276 m3 between 2005 and 2020. It envisions that the component of wa- ter imported from the Metropolitan Water District will be reduced to half of what it was in 2005 and that conservation measures, including the elimination of perco- lation losses through canal lining, as well as the reliance on local sources and recycled water will all grow significantly (see Figure 3-11). In addition, it envisions that there would be a substantial component of desalinated seawater added to the portfolio. The target portfolio illustrates how the mix of sources of water avail- ability can be diversified and can include a balance between old sources and new sources, demand management and supply augmentation, new supplies and recycled supplies, and the partial substitution of less remote supplies (from the Imperial Irrigation District) for more remote supplies (from the Metropolitan Water District). Conservation, 10% MWD Transfer, Seawater 24-33% Desalination, 6-15% Recycled Water, 6% Local Surface Water, 9% Groundwater, 6% IID Transfer, 21% Canal Lining Transfer, 9% FIGURE 3-11: Water supply portfolio for San Diego in the year 2020. SOURCE: Robert Yamada, San Diego County Water Authority, personal com- munication, 2006. Desalination is an option to be considered, on balance with other al- ternatives, when planning for future water supply shortages. The addition of desalinated seawater to a water supply portfolio provides a source of ânewâ water, whose reliability is not linked to hydrologic variability (i.e., droughts). Of course, a water supply portfolio that is unbalanced in any direction can carry unexpected risks. Although the addition of desalina- tion facilities can improve reliability under some circumstances, exces- sive reliance on desalination may have important energy implications in regions with constrained or unreliable energy supplies. Centralized de- salination facilities may also carry security or seismic risks that require special attention.
Water for the Future 57 CONCLUSIONS AND RECOMMENDATIONS Long-term decisions about whether to pursue desalination facilities, other supply alternatives, efficiency improvements, reallocations and water transfers or trades, or other management policies hinge on many factors. While efforts to identify new, untapped sources of supply have dominated water policy for the past century, traditional sources of supply are increasingly expensive, unavailable, or controversial, raising new interest in desalination as a source of high-quality reliable supply. At the same time, however, new thinking about water demand and forecasting may be fundamentally reshaping the water debate by forcing a reevalu- ation of basic assumptions of ever-increasing water demand. Indeed, to- tal water withdrawals in the United States have remained stable in recent years, despite growing populations and economy. Changes in patterns of water consumption and withdrawals mean that past patterns of water use will not always be a reliable guide to the future. Satisfying future water demands requires integrating new factors and concepts into water planning, scenarios, and investment decisions. In particular, the assumption that water demands will inevita- bly parallel population and economic growth no longer appears to be cor- rect, and rethinking this assumption offers new possibilities for water providers. Most forecasts of future water demand have been unduly con- servative and have failed to account for the fact that consumptive water use and withdrawals do not inevitably grow as population and economies grow. Total water use in the United States, including most regions and most sectors, has declined in recent decades. If these trends continue, pressure to identify new sources such as desalination may also decline, or at least be concentrated in particularly water-scarce regions or where users are able and willing to pay for high-quality, reliable new supply. Desalination, using both brackish and seawater sources, is likely to have a niche in the water management portfolio of the future. The advantages of desalination, such as high reliability and insensitivity to natural hydrologic variability, are real but difficult to quantify and should be considered in any decisions among a âportfolioâ of water management options. The significance of this niche, however, cannot be definitively determined at this time, because it will depend on a host of complicated and locally variable social, economic, environmental, and political fac- tors, including societal preferences, the costs and reliability of alternative sources of supply, and the availability of cost-effective, environmentally
58 Desalination: A National Perspective sustainable concentrate management options. In the complete absence of these factors, the theoretical potential for desalination is effectively unlimited. Large quantities of inland brackish groundwater appear to be available (see Chapter 5) and, in coastal areas, ocean resources are essen- tially infinite in comparison to human demands. But, as with most re- source questions, the theoretical potential and the practical potential are far different. The technological capabilities and the economic, social, and environmental constraints are discussed in detail in Chapters 4-7.