A Review of Reliability Analysis for Water Quality in Water Distribution Systems

Abstract

A review of reliability research for water distribution systems demonstrates that, to date, little is currently available characterizing water quality reliability indices. The incidence of microorganism caused outbreaks of waterborne disease demonstrates a number of causes, most of which are the result of water treatment system deficiencies. However, the basis for a change in this situation is projected as a result of the increasing age of distribution system components, increasing urban populations, per capita water demands, and deterioration of water distribution infrastructure. Although there is no universal agreement on how to define, or measure, the reliability of a water distribution system, this Chapter reviews the alternatives for characterizing reliability, demonstrating some of the strengths and weaknesses, and provides areas of future research. Water Distribution System Reliability 108 conditions. This means that for a reliable water supply system, water must be (i) available on demand, (ii) delivered at a sufficient pressure for proper use, and (iii) safe in terms of quality. Although reliability of a water supply system in general is a measure of performance in terms of the three factors indicated, undesirable events/failure will occur which will cause a decline or interruption in system performance. The reliability of a water supply system can be considered under three types of failure: mechanical, hydraulic and water quality failure. Mechanical failures, also termed component failures, may, for example, be pipe breakage, pump failure, power outages, or control valve failure. Changes in demand or in pressure head may result in hydraulic failures. These failures may be due to, for example, old pipes with varying roughness, inadequacy in pipe size due to increased water demands, insufficient pumping capacity, and insufficient in-system storage capacity. Water quality failure may be defined as occurrences where the concentrations of contaminants exceed the maximum contaminant level (MCL) defined by water quality standards. The major concern for water quality failure is the adverse effect on the health of humans. Due to the importance of water supply systems for the needs of society and for industrial growth, reliability studies have become of increasing importance for water distribution systems where considerations of planning, design and operations are integrated. However, quantifying the reliability of a water supply system continues to be a major problem. For confident decision-making, a set of meaningful and appropriate reliability measures need to be defined, wherein all the measures must be computationally feasible. Reviews of the literature by Mays (1996) and Engelhardt et al. (2000) revealed that that there is no universal agreement on how to define, or measure, the reliability of a water distribution system. This Chapter reviews the alternatives for characterizing reliability, demonstrating some of the strengths and weaknesses, and provides areas of future research. 7.2 Reliability Index Altho...

System-wide joint-dynamic-response approach to water quality evaluation in distribution networks with multiple service reservoirs and pumps

“…This may be one of the reasons that satisfactory integrated service reservoir design optimization models are not available yet. Huang et al [26] stated that research on water quality reliability has generally been very simplistic and comprehensive measures and protocols were required. For example, Atkinson et al [1] discussed the maximum and "average system water age".…”

“…Studies on the deleterious effects of service reservoirs and a clear understanding of the system-wide response are lacking. Optimization models for water distribution networks with multiple service reservoirs have not addressed water quality concerns adequately, and rigorous comparisons of candidate solutions are not available [26]. A quantified robust framework [26] will help to improve: (a) investment decisions [59],(b operational control [59],and (c) the development of water quality-based design optimization models [18,28].…”

“…Optimization models for water distribution networks with multiple service reservoirs have not addressed water quality concerns adequately, and rigorous comparisons of candidate solutions are not available [26]. A quantified robust framework [26] will help to improve: (a) investment decisions [59],(b operational control [59],and (c) the development of water quality-based design optimization models [18,28]. While previous investigations considered the individual service reservoirs or demand nodes in isolation, this article develops and demonstrates the benefits of a system-oriented approach to the evaluation of water quality that transcends the single-event regulatory compliance paradigm.…”

Complex Networks Theory for Evaluating Scaling Laws and WDS Vulnerability for Potential Contamination Events

“…In the few last years, Water Safety Plans (WSPs) have been recognized a valid tool for a thorough identification of the various hazards and related impacts on a WDS [1,2], allowing water managers and public institutions to perform global risk assessment and to prioritize control measures and strategic interventions in order to enhance overall reliability [3,4]. In this context, many studies have focused on quantitative resilience and robustness evaluation (recent reviews are in [5,6]), but less on reliability analysis for water quality (see [7] for a review).…”