Special Issue on the Battle of Background Leakage Assessment for Water Networks

The concepts of sustainability and resilience should drive modern management of infrastructure systems (ASCE 2013a), in addition to efficacy and efficiency. Engineers have a leadership role and responsibility to provide effective and innovative solutions in addressing the challenges of sustainability (ASCE 2013b). Water distribution networks (WDNs) are infrastructure systems with high economic, social, and environmental value, and pursuing sustainability in WDN management means to ensure adequate water supply to people, while minimizing the waste of water and energy resource. Unfortunately, nowadays urban WDNs in the United States and Europe are facing the replacement era (AWWA 2011) because most urban WDNs are approaching the end of their service life since their building ex novo and/or expansion after World War II. Both the increasing rate of water pipe bursts [i.e., it is estimated that 240,000 water mains break per year in the United States (ASCE 2013a)] and the rise of water leakages demonstrate such trends in WDNs. Since 2006, the World Bank estimates that the cost of nonrevenue water is about 14 billion US$ per year (Kingdom et al. 2006), and most of these represents real water outflows classified as bursts or background leakages (Lambert 1994).

Reducing background leakage in urban WDNs means to save water resources and reduce the carbon footprint for water abstraction, treatment, and pumping, while reducing the risk of pressure deficit and increasing asset longevity (European Commission 2013). In fact, most pipe burst events, which cause major road and service disruptions, possible damages to private properties, and unplanned works, often begin as background leakages, which in turn depend on both asset deterioration and WDN hydraulic status.

Actually, the massive renewal of WDNs is neither technically feasible, because of their pervasiveness in urban areas, nor economically sustainable, because of the scarce funds available compared with the large extent of deteriorated water pipelines. Water utilities ask for integrated strategies for leakage reduction coupling structural and nonstructural/operational actions. Depending on the WDN hydraulics, asset, and topology, some technical options consist of resizing/renewing pumping stations, increasing the capacity of tanks, scheduling of pump operation or pressure control, even by modifying water paths closing gate valves.

The complexity of such technical problems in large WDNs is a challenge for engineers and requires significant advancements in methodologies and tools to support WDN management. The paradigms used so far to analyze and operate new water distribution infrastructures show many limitations in supporting the management of aged WDNs. For example, the hydraulic models based on the assumption of fixed water demands (e.g., EPANET 2, Rossman 2000), independent on pressure, prevent from assessing actual WDN capacity under pressure deficit scenarios. In addition, they preclude the assessment of pressure-dependent background leakages (Giustolisi et al. 2008) along the pipelines, which are essential to simulate the effects of pipe replacement of WDN system functioning.

In the last three decades, the technical-scientific research in the WDN area has produced a number of achievements in both WDN hydraulic modeling and strategies for effective infrastructure optimization, also exploiting interdisciplinary areas like graph theory or artificial intelligence. Furthermore, the pervasive application of information and communication technologies also in the water sector is opening many possibilities for sustainable and reliable WDN management, as part of the smart city paradigm.

The Battle of Background Leakage Assessment for Water Networks (BBLAWN) was designed as a competition within the 16th Water Distribution Systems Analysis Conference (WDSA 2014), held in Bari (Italy) in 2014. Like previous battle competition series dating back to 1985, the BBLAWN was conceived to stimulate experts from academia, research centers, industry, and consulting firms to propose alternative approaches for reducing water losses and saving energy in a case study WDN, considering the possibility of asset renewal and system strengthening. Each team presented a methodology to support planning of asset renewal, structural improvement works, as well as pressure management using pressure control valves and alternative pump scheduling, considering the financial sustainability of relevant actions. The case study of C-TOWN, already used in previous battle editions, provided a sufficiently complex benchmark to demonstrate innovative approaches and discuss them from an engineering perspective.

The complexity of the problem and the different approaches and modeling tools proposed made the BBLAWN at the WDSA 2014 conference an invaluable opportunity for exposing innovative approaches to water utilities worldwide. With the aim of performing a technology transfer from current technical-scientific research to the real WDN management field, this Special Issue collects contributions from 13 teams that took part in the BBLAWN. In addition, an introductory paper (Giustolisi et al. 2015) authored by the organizers of the BBLAWN is included to summarize the technical problem and provide a further contribution to the discussion.

The lesson learned from BBLAWN is that a unique best solution for such a technical problem does not exist, but effective strategies require a combination of engineering judgment, computationally effective multiobjective optimization strategies, and realistic advanced hydraulic models.