develop economically, and such economic growth could be substantial in Jordan and the West Bank and Gaza Strip. The twin phenomena of population and economic growth will place increasing pressure on the already limited water supplies of the region. The region's success in managing this intensifying water problem will largely be a matter of how it identifies and accounts for all of the many factors that determine and influence water use.
This chapter reviews the factors that are likely to influence future water use, giving special consideration to practices that may be amenable to some degree of change. The chapter's discussion begins with the difficulties of projections and the problems associated with identifying specific disparities between water supply and demand.
Water resource planners frequently focus on identifying potential gaps between water demand and water supply at some future date. Detailed plans are then developed to ensure that supplies are brought into balance with anticipated demands, thereby eliminating the gap. Such plans typically include projections of anticipated levels of water use based on population growth, per capita and per hectare water use, and other variables that affect demand. These estimates of future use are then compared with existing levels of available water supplies, and the time when a ''gap" or disparity between anticipated levels of use and existing levels of supply is identified. Based on the size and timing of this gap, measures and actions are then identified to close the gap and bring supplies into balance with the expected demands. There are many examples of this planning methodology (California Department of Water Resources, 1994), including many of the water planning analyses for the study area (see, for example, CES Consulting Engineers and GTZ, 1996).
The committee believes that water planning approaches that initially focus on emerging gaps between supply and demand are flawed. They are based on projections that, however well informed, often ignore the considerable uncertainty surrounding future levels of water use; and more generally, such plans are always based on a significant number of assumptions, many of them untested and unstated. To the extent that water availability determines population and economic growth, projections can become self-fulfilling prophesies. By contrast, where economic and population growth are only weakly determined by the availability of water, overly optimistic growth projections may lead to investment in excess water supply capacity, the costs of which must be borne, regardless of whether the water is used. In circumstances characterized by significant