**3. Discussion**

The interest of researchers for the Special Issue was high with 14 published papers (4 review papers and 10 research papers).

The review papers showed that some topics, such as innovative procedures for water network partitioning [18], smart meters and tools for water demand measuring [19], end use disaggregation and forecasting [9], and applications for cyber-security [15] are already available for water utilities. However, as appropriately reported in [4], and confirmed by [15], more coordination between academia, industry, and government is required to guide real world deployment of smart urban water systems. In order to meet the demands of industry and government and successfully turn this new paradigm into practice, the researchers [4] showed that it is necessary to obtain a consensus from conceptual, technical, and practical perspectives. However, also for more consolidated innovations (like softwares, best practices, and procedures) no comprehensive consensus exists. Accordingly, the fivelayer framework proposed by the authors aims to simplify the implementation of smart water technologies in novel solutions and case studies, and, for the first time, to better characterize the peculiar features of smart water systems.

Besides presenting new approaches and solutions to smart water networks, the works presented in this SI also highlight the open challenges that should be prioritized in future research.

First, the achievement of a shared definition of resilience of water systems and a shared formulation performance indices for the management represent a key priority to further advance the concept and standardization of smart water networks. In fact, with the help of smart meters and the analysis of big data it will be possible to define novel metrics and consequently improve calibration phases and maintenance plans and better face water crisis periods through water demand management. With reference to the latter point, this Special Issue highlights that the technologies and the methodologies proposed are mature to start pilot sites on a large scale. It is worth highlighting that in [4] was identified that widely applied concepts of resilience of urban water infrastructure are lacking smart components and that there is a need for novel concepts for smart water systems as these are even more complex than traditional systems. By defining two conceptual metrics (smartness and cyber wellness), a first step in this direction was taken, but comprehensive further research is required to successfully tackle these short-comings in current smart water applications.

Further, the more advanced challenges delineated in the SI are the topic regarding real-time control and operation of water systems, also with the possibility to activate dynamic changes in the network operation using smart devices controlled in real-time (e.g., regulation valves, on-off valves).

The availability of a large amount of data collected by smart sensors in IoT framework brings up valuable information and knowledge from the system and speeds up the spreading of data-driven applications in water industries. Some solutions offer new visions when well calibrated hydraulic models are difficult to obtain. In these cases, it could be possible by analyzing the learning system behavior only using data collected from hydraulic, maintenance, and economic information (i.e., length of pipes, diameter, type of material, age, flow, costs, etc.) and the know-how of the operators recorded in maintenance journals (i.e., date and time, type and causes of disservice) without any physical modelling. This aspect is very interesting and data-driven approaches also represent a new challenge for the future of smart water systems.

#### **4. Conclusions**

This Special Issue shows that the multi-faceted paradigm of smart urban water networks can be declined in different ways and applications. While the digital transformation of water networks still presents several open challenges, many solutions can be considered ready to be implemented by water utilities and operators. However, the technological transfer from research laboratories to the water market is still slow for many reasons, mainly due to the delay of the standardization processes and a common regulatory framework.

Overall, the papers collected in this SI offer to the technical and scientific community a wide overview of the solutions and possibilities offered by the implementation of smart meters, IoT, innovative modelling, and simulation approaches fostered in the last years by the availability of high computational power and new digital technologies. The digital transition of water networks towards smart systems is an ongoing and incremental process. Yet, radical changes have been already observed in the last years and more advances leveraging the state of the art, including the contributions presented in this SI, can be expected if a *new deal* between academia, industry, and governments will be embraced to reap and materialize all the benefits of the digital transformation.

**Author Contributions:** Writing—original draft preparation, A.D.N. and R.S.; review and editing, all authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no direct external funding.

**Institutional Review Board Statement:** The study did not require ethical approval.

**Informed Consent Statement:** No required.

**Data Availability Statement:** Not applicable.

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

#### **References**

