# Towards Digitalization of Water Supply Systems for Sustainable Smart City Development--Water 4.0
## 1 Introduction  
Water is an important component of economies today and is needed in nearly all modes of production. It is a fundamental resource utilized in virtually every modern industrial process and provides an essential element for urban development across the country. Hence, it is important to ensure that everyone has access to clean and pollution-free water, which is a duty of the municipal water service or water utility. Water utilities are saddled with the responsibilities of supplying potable water to end users in accordance with objective six of the United Nation's sustainable development goals. This is achieved through the use of water supply systems (WSS). WSS operations require the delivery of potable water to end consumers via a vast and complex network of distribution piping systems. Water utilities worldwide face increasing challenges to ensure sustainable water distribution to the end consumer. These challenges stem from burgeoning populations, the dynamic nature of water supply distribution systems owing to the effect of climate change and consumer demand uncertainties, as well as the frequent level of water losses in systems. Modern water supply networks are complicated, dynamic in nature and hard to manage owing to the stochastic nature of water demand. They comprise a complex network of pipelines (see Figure 1) buried underground for several years and are not readily accessible. Thus, due to ageing, corrosion issues and third-party damage, cracksoccur along the pipes, which causes loss of significant volumes of water. One of the major problems affecting water supply system operations is water loss due to leaking pipes. Even in a new system, background losses may occur at the pipe fittings and cross-connections point and run continuously through the entire lifespan of the piping network [1,2]. Since they are underground large structures and not readily accessible, monitoring becomes a serious challenge. In a severe situation, the problem becomes more complex when leaks occur at several points along the pipes. In fact, it is crucial to localize pipe leaks as quickly as possible after the occurrence and pinpoint the leaks' hotspots to perform active maintenance in the region of high leak occurrence in the network. On an annual basis, there is a dramatic increase in the investment cost for leak detection and repair [3]. This is because its maintenance rate increases exponentially once a pipe's length starts to require maintenance [4]. Other issues affecting the smooth operation of water supply systems include pressure control, water demand management, pump scheduling, operational planning and control, and water security as reported in [5], among others. Furthermore, the financial losses, improved maintenance cost to repair leaky pipes and the increased energy expenditure required to feed the leaks are major problems caused by water losses [6, 7, 8, 9, 10]. Considering the latter, the occurrence of a leak requires more energy to maintain desired service levels [6,7]. That is, more energy is required to pump water to meet specific demand at a node. This escalates the cost of energy due to extra pumping of water. Consequently, a relatively high cost associated with pumping due to leaks is one of the problems caused by water losses. Thus, the operation of water supply distribution systems usually requires a large amount of energy, which varies with respect to the characteristics of the region served [11]. For instance, in the United States it was estimated that about 10 billion kWh of power generated is budgeted towards water losses annually [12]. The water quality may also be compromised. This is because leaks introduce infections into a water supply system operating under low-pressure conditions [9,13]. This increases the risk of water quality deterioration, which also prompts the need to assess the water contamination level in the system. Therefore, it is of paramount importance to address the issue of water losses in water distribution networks (WDNs).