Desalination A National Perspective (2008) / Chapter Skim
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3 Water for the Future
3 Water for the Future
Pages 38-58
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From page 38... ...
. 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 endangered delta smelt (Ricci and Bailey, 2007)
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From page 39... ...
Seawater desalination technology is unique among supply augmentation 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 supplies during short-term droughts, although longer periods of drought can affect regional groundwater availability.
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From page 40... ...
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 control floods, move water vast distances, disinfect and treat water supplies, and deliver water for irrigation or hydropower.
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From page 41... ...
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.
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From page 42... ...
Both total U.S. freshwater withdrawals and gross national product exhibited rapid growth until the late 1970s (Figure 3-1)
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From page 43... ...
Gross national product (GNP, in billions of 1996 dollars) and total water withdrawals (cubic kilometers per year)
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. Total water withdrawals based on data from MacKichan (1951, 1957)
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From page 45... ...
Reductions in water withdrawals for thermoelectric power production have been driven by the gradual replacement of once-through cooling systems with systems that recycle water (Figure 3-3)
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From page 46... ...
. Total water withdrawals in California 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.
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From page 47... ...
Water use in the city of Seattle. SOURCE: Data from Seattle Public Utilities (2007)
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From page 48... ...
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 concentrations 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.
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From page 49... ...
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.
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From page 50... ...
, U.S. Senate Select Committee on National Water Resources (1961)
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From page 51... ...
As a result, Seattle's 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.
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From page 52... ...
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 unchanged (see Box 3-3)
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From page 53... ...
The most desirable quantities and prices for water supply are not always strictly determined by the elements of economic supply and demand, although those elements will always be important determinants of water sufficiency. Departures from strict supply and demand solutions may be caused by (1)
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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)
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From page 55... ...
. 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.
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From page 56... ...
SOURCE: Robert Yamada, San Diego County Water Authority, personal communication, 2006. Desalination is an option to be considered, on balance with other alternatives, when planning for future water supply shortages.
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From page 57... ...
At the same time, however, new thinking about water demand and forecasting may be fundamentally reshaping the water debate by forcing a reevaluation of basic assumptions of ever-increasing water demand. Indeed, total water withdrawals in the United States have remained stable in recent years, despite growing populations and economy.
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From page 58... ...
Large quantities of inland brackish groundwater appear to be available (see Chapter 5) and, in coastal areas, ocean resources are essentially infinite in comparison to human demands.
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