**1. Introduction**

This Editorial presents the paper collection of the Special Issue (SI) on Smart Urban Water Networks. The number and topics of the papers in the SI confirms the growing interest of operators and researchers for the new paradigm of Smart Networks as part of the more general Smart City. The SI showed that digital information and communication technology (ICT), with the implementation of smart meters and other digital devices, can significantly improve the modelling and the management of urban water networks, contributing to a radical transformation of the traditional paradigm of water utilities. The paper collection in this SI includes different crucial topics such as reliability, resilience, and performance of water networks, innovative demand management, and the novel challenge of real time control and operation, along with their implications for cyber-security. The SI collected fourteen papers that provide a wide perspective about solutions, trends, and challenges in the contest of smart urban water networks. Some solutions have already been implemented in pilot sites (i.e., for water network partitioning, cyber-security, and water demand disaggregation and forecasting) while further investigations are required for other methods, e.g., the data-driven approaches for real time control. In all cases, a *new deal* between academia, industry, and governments must be embraced to start the new era of smart urban water systems.

The deployment of digital information and communication technologies (ICTs) in different aspects of urban life has contributed to generating the notion of the Smart City [1], recently recognized in the scientific and technical international community as a city where the use of ICT allows making "the critical infrastructure components and services—which include city administration, education, healthcare, public safety, real estate, transportation, and utilities—more intelligent, interconnected, and efficient" [2]. The implementation of new monitoring and control sensor technologies and the availability of high computational power changed the traditional approach to studying, designing, and managing water

systems and enabled the development of new data-driven approaches fed by big data. The availability of low-cost devices, controlled by remote systems, is pushing the operators of urban water systems to fill the technological gap with other network utilities (i.e., electricity, gas, Internet, etc.), as reported in [3]. This transformation, triggered by ICTs, has also generated the new concept of the smart water network (SWAN) as a key subsystem of the Smart City.

In the more general framework of Industry 4.0, the recent development of Internet of Things (IoT) technologies applied to smart grids opens further novel opportunities in the management of water network systems and beyond. At the current state, it is possible to imagine novel solutions based on digital innovations to study, analyze, assess, and improve traditional approaches for leakage reduction, pressure management, optimal maintenance, water quality protection from accidental and intentional contamination, network calibration, water use identification, water demand modelling and management, water network partitioning, adaptive and dynamic control, as well as the new challenges raised in the digital era (e.g., cyber-security). This leads to a transformation of the traditional operational criteria and contributes to an increase in the resilience of urban water systems. In addition, by analyzing the cross-links between the urban water infrastructure and other systems (i.e., power grids, urban drainage, smart homes, etc.) it is possible to account for multi-sectoral interconnections in planning and management decisions for more resilient Smart Cities.

The objective of this Special Issue is to gather contributions advancing scientific and technical methodologies, technologies, and best practices that advance smart urban water networks by leveraging the increasingly available computational power in simulation, IoT systems, and smart meter devices. Through this open access journal, a wide community of researchers, operators, and water utilities can have access to a collection of recent cuttingedge contributions showing how some key operational challenges of water networks can be improved by coupling ICT technologies, physically-based mathematical procedures and data-driven techniques (i.e., identification, optimization, complex network theory, etc.). In other terms, this will foster the digitization of urban water networks towards the concept of smart cities and societies.

The papers in this Special Issue provided heterogeneous contributions to the topics proposed by the Editors in the call, showing a large variety of implemented and potential solutions, current trends, and challenges that remain open for future research. In the following sections, the paper collection is presented, highlighting the main proposed novelties.

## **2. Special Issue Paper Collection**

The keywords suggested by the Editors of this Special Issues tried to identify some potential fields of applications that are being transformed by digital innovation in smart urban water networks. In this editorial, it is worth reporting some of them to attest the effort of synthesis and offer to researchers and operators a possible map of innovation in current cutting-edge research on urban smart networks, with topics including: optimal network design and management, novel modeling approaches, application of IoT, adaptive automatic control of urban water network, machine learning and big data for water utilities management, characterization and modeling of water demands at different spatial and temporal scales, divide-and-conquer techniques for water network partitioning, innovative metrics for resilience computation, actions to protect water distribution network from accidental and intentional contamination, novel approaches for water safety plans, data-driven water demand modeling, non-intrusive load monitoring, water and energy nexus, end use disaggregation of water consumption, water demand user profiling, behavioral modelling and water-energy demand management, innovative decision support systems, hydroinformatic applications, innovative intermittent uses in drought periods, pump and turbine implementations, disaggregated pricing and tariff policing, and cyber-security applications.

Many of these concepts were addressed and discussed in the papers collected in this Special Issue, which was mainly dedicated to water distribution networks but, as will be shown below, also hosted some contributions on water drainage systems, highlighting how the digital transition is affecting all subsystems involved in the urban water cycle.

Specifically, the Special Issue on Water Journal collected 12 papers, which in this editorial and, consistently, in the on-line paper collection, are categorized in four main topics: (1) Reliability, Resilience, and Performance, (2) Smart Urban Water Demand Management, (3) Smart Real Time Control and Operation, and (4) Cyber-Security in Water Systems.

Two further contributions bring the total number of submitted papers to 14: a timely review on the Smart Water Systems, inserted as the overview of the Special Issue; and a review on the state-of-the-art literature on cyber-security in the water sector, which systematically presents the existing works in this fast growing field and identifies outstanding issues.
