Evaluating reliability and efficiency of water distribution networks

Aim of the paper is to introduce a new approach in the evaluation of overall per-formance of water distribution networks, taking into account both reliability and efficiency. The first is calculated through long-term quasi-steady simulations in which mechanical failure of system components (like pipes or pumps) and hydrau-lic failure (related to demand and pipe roughness variations) may happen. The se-cond is defined as the ratio of the total amount of actually delivered water and the overall input volume, with reference to the same time horizon. Research has been divided in two phases. In the first, a system is analyzed introducing pressure-dependent delivered discharges: several simulations have been carried out in or-der to assess the influence of failure rate, required pressure, and roughness varia-tion on reliability. In the second, the concept of efficiency is introduced, and simu-lations have been repeated with the aim of analyzing the influence of leakage rate: the system overall performance has been defined as the product between reliability and efficiency. The methodology has been applied to a real system: results show how a highly reliable network can be characterized by low performances, especial-ly when the leakages of the system are of the same order of magnitude of the total input volume.