*2.2. Reliability, Resilience and Performance*

Some papers of the Special Issue deal with the subtopic of reliability of water networks. In these papers, some specific water network management issues, including network partitioning, and protection from contamination and other critical events are addressed, and a comparative analysis of some reliability indices was also provided.

Another interesting problem faced in the Special Issue is the optimization of fault examination in water distribution networks. It is essential to automatically detect faults (e.g., leaks, blockages) in water distribution systems to avoid or reduce the loss of resources, non-revenue water, and operational costs. In [5] was proposed an inverse transient-based optimization approach to identify such faults. They tested their approach with models of two hypothetical water distribution systems and found that their algorithm is proven reliable and efficient in detecting faults. In the paper [6], the authors reviewed the stateof-the-art literature on water networks partitioning in district metered areas (DMAs) and provided a comprehensive overview of existing methods and approaches. They classified these methods in two steps: clustering algorithms (dividing the network) and dividing procedures (identifying the optimal positions of gate valves and flow meters). Six of the most widely adopted clustering algorithms were presented and discussed in-depth, and future research gaps were identified (e.g., considering devices, such as pumps, operations under abnormal conditions).

Furthermore, [7] presented a strategy for reducing the impacts of contamination events in water distribution systems. The authors developed a hybrid strategy which is based on water network partitioning and the installation of sensors. By testing the framework on a real water distribution system, they showed how to reduce the impact of any kind of critical events.

Finally, in the literature, there are numerous reliability indices to evaluate the performance of water distribution systems. However, the choice of which one to use is often challenging, as they rely on different assumptions and some of them are correlated. In this regard, a very useful comparative analysis of reliability indices and hydraulic measures was carried out by [8], who investigated nine different reliability indices and six different

hydraulic measures with 17 hypothetical networks with various topological features under different supply scenarios. They found that selecting the indices according to the defined goals is essential and, accordingly, give guidance on how to choose the right indices for different water network configurations.
