A Water Distribution System (WDS) that is structurally inadequate in fully satisfying the water required by customers needs to be rehabilitated in order to restore the required performance. However, a problem that frequently arises in this analysis is the selection of which solution should be adopted in order to provide a suitable service and, simultaneously, in minimizing rehabilitation costs. This decision can be facilitated by considering the water required by users but not supplied to them because of the structural inadequacy of the system - representing a source of lost revenue for the water companies. This cost is a function of the level of inadequacy of the hydraulic system and of the unit cost of the water. On this basis, safeguarding the hydraulic reliability of a WDS also implies a reasonable rate of return on the water company’s capital investment. Accordingly, a novel, archiving multicriteria optimal approach to a stochastic rehabilitation problem for WDS, has been formulated and solved. The objectives considered are the minimization of the total rehabilitation cost (sum of the structural costs and the lost revenue costs) and the minimization of risk. The latter is defined as being the product of the probability of failure in satisfying the water demand and the consequence of this failure, i.e. the total volume of water not delivered. A probabilistic approach is used to characterize demand uncertainties within the optimization model. The relevant probability density functions and their parameters have been estimated through an experimental study conducted on a real-life WDS and a Pressure Driven Demand extension for the EPANET hydraulic solver has been employed in order to model the deficient water distribution system. The methodology is been applied to several case studies and relevant conclusions are drawn in order to assist the decision maker in the selection of the optimal rehabilitation solution.
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