This definition completes the one given by the Brundtland Commission, since it links: i) the present needs with society's objectives, ii) the needs of future generations with
environmental integrity. Furthermore at river-basin or regional levels, it may not be possible to meet the needs or demands of even the present generation, let alone future ones, if these needs or demands are greater than what the basin or the region can afford. Moreover, degrading the water resource systems will reduce their capacity to meet future needs, whatever those needs will be. So, demand management and degradation prevention play a role of paramount importance in this new concept of sustainable development.
While it may never be possible to determine with certainty whether a water resource development project is sustainable or not, it is possible to devise some procedures that allow to compare performances of alternative options with respect to sustainability. Work conducted on sustainability evaluation has two main emphases (Dorcey, 1992; Duckstein and Parent, 1994, Kroeger and Simonovic, 1997). The first defines sustainability indicators, as conditions strictly associated with sustainable development, so that their presence is indicative of its existence. The second develops criteria for measuring sustainability such as fairness, reversibility, risk and consensus. Sustainability indicators and/or criteria should be included in the evaluation of water resources engineering projects. The inclusion of such parameters will lead to extending the decision-making process beyond the consideration of purely economic factors alone, toward the development of an evaluation procedure that reflects the new paradigm of sustainability. The ultimate implementation of such a decision-making framework will require a multi-objective approach to conjunctive use project selection, which must consider the trade-offs between traditional environmental and economic factors and