As population and regional economies grow in the future and as the importance of providing water to support environmental services becomes more widely appreciated, the overall pressure on the nation’s limited 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 water 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 especially costly. However, recent advances in technology, especially improvements in membranes that can be used in desalinating both brackish water and seawater, have rekindled more widespread interest in desalination. 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 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. The recent occurrence of severe droughts in many areas of the country and the prediction that global climate change will likely result in regional increases in the frequency and intensity of extreme events have heightened public sensitivity to the variability 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 considerable interest, therefore, in advancing desalination technology and concentrate 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 concept of water availability, use, scarcity, and sufficiency. Trends in U.S. and regional water use are presented along with a review of experience



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