# Development of Practical Design Approaches for Water Distribution Systems
## 1 Introduction
In addition, the red water problem in Incheon (2019.05, South Korea) caused approximately 10 billion KRW worth of material and serviceability damage to water users. For these reasons, the various design factors (e.g., system reliability, resilience, robustness, redundancy, energy consumption, and environmental factors) should be considered simultaneously. Therefore, practical WDSs design approaches should consider multi-objective optimization considering not only cost but also reliability, especially against accidents (shutdown of pipes and pumps) and uncertainty in spatial and temporal demand forecasts [12; 13; 14]. [PERSON] et al. [15] confirmed the use of \"robustness\" (i.e., the coefficient of variation of stochastic pressures) to enhance the minimum cost design approach. This study performed consistently under uncertain failure conditions (i.e., pipe burst and fire flow) that were not considered in the design phase for finding best pipe diameter set. [PERSON] et al. [16] were the first to develop the robustness indicator, which explicitly incorporates variations in stochastic pressure. It was maximized while minimizing the total system cost in their WDSs design model. The model was calculated by the residual between the average pressure head and minimum pressure head divided by the standard deviation of stochastic pressure heads. Therefore, the proposed multi-objective WDSs design seeks a design solution with high average pressure and low-pressure variations to maximize. [PERSON] et al. [13] proposed a robustness-constrained WDSs design and operation model to minimize total pump construction and operation costs with a constraint on the level of operational reliability. In their study, the system operational robustness measure was defined as the maximum value of nodal daily maximum pressure differences in the system. This was converted to dynamic system performance under unsteady conditions. The study confirmed that constraining the pressure variations in a day led to the installation of a greater number of small pumps than the least-cost approach did, in which a few large pumps were constructed. A non-linear trade-off relationship was identified between the daily maximum pressure difference and total pump construction and operation costs. [PERSON] et al. [17] applied the optimal valve installation to practical WDSs design. They developed a valve installation method that prioritizes segments based on segment total demand and the existence of important public facilities (e.g., hospital, elderly center, fire station), and selects the segments where valves should be installed to minimize the maximum undelivered segment demand under pipe break conditions. According to existing research into practical WDSs design, the design approach should reflect the construction condition (i.e., pipe continuity) and consider various design factors such as system performance measure. This study improves upon past optimal WDSs design approaches, which considered pipe continuity. To accomplish this objective, this study proposes an improvement of the practical design technique with pipe connectivity constraints for efficient WDSs construction under a multi-objective optimization framework. To validate the proposed model, the approach is evaluated using differently configured WDSs benchmarking problems (i.e., the Hanoi and Fossolo networks) and real-world WDSs. The application of this practical design technique, which considers pipe continuity and multiple design factors, can reduce the gap between the real-world and theoretical design by accounting for construction conditions and abnormal situations.