**6. Conclusions**

A new P&P technology, coupling a PAT and a pump, has been studied on the basis of the experimental data of the pump working in direct or in inverse mode. A P&P is suitable in all cases when a certain amount of the water at the end of a water supply system, presenting a residual energy, has to be pumped to a second network at a higher pressure level. In such a case, P&P is a low cost technology allowing the recovery of the residual energy of the water in the first network and the increase of the pressure level of the water in the second network. Equations for P&P design have been presented, allowing a simple analysis of the P&P working conditions. Depending on the number of stages of the pumping, different operating conditions in the ancillary supply network can be obtained, in terms of water demand and pressure level. For the pump model used in the simulation, up to 40% of the water can be transmitted by the P&P to a pressure level 20% higher than the initial level. If the water to be transmitted is limited to 20%, the pressure level can be increased by the P&P by more than three times. This high potentiality is determined by the total efficiency of the P&P, even greater than 40%. The case study shows the viability of the system in different scenarios, considering different supply conditions as well as different values of turbined discharge. The results, depending on the network configuration and the considered scenario, show that the P&P system can completely replace an ordinary pumping system or supply the network when the available hydraulic power is high. The calculated annual energy saving demonstrates the economic relevance of the P&P plant. As a future implementation of this study, an experimental investigation on a laboratory prototype could be undertaken and the results would be used for the design of a full scale plant, to investigate the interactions with a WDN in a real situation.

**Author Contributions:** Lauro Antipodi and Oreste Fecarotta performed the experiments on the PAT and on the pump. Armando Carravetta, Oreste Fecarotta and Umberto Golia developed the mathematical model. Umberto Golia ran the simulations. Armando Carravetta and Oreste Fecarotta wrote the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
