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The intermittent water supply (IWS) of water distribution systems is a common practice caused by the imbalance between available water resources and customers' demands. Transition to the continuous water supply (CWS) is desirable to reduce quality, equity distribution, and pipe integrity issues but is often practically unachievable in the short or medium term. The World Bank funded a laboratory activity at the Water Engineering laboratory of the University of Perugia, Italy, to investigate how remedies can be introduced to mitigate the impacts of IWS and preserve pipe integrity, facilitating the transition from IWS to CWS. The results of the tests with different feeding conditions, downstream outflows, and air valve dimensions and locations are described and discussed in this paper, culminating in typical interventions that can be implemented to reduce, if not completely eliminate, the undesirable consequences. Plain Language Summary: Almost one billion people worldwide are estimated to receive water intermittently, especially in low‐ and middle‐income countries. Intermittent supply has a significant impact on the water quality, equity of water distribution among users, accuracy of the customer meters, and the structural condition of the pipes. Water distribution systems are not usually designed for such an operating approach, and interventions are required to preserve the pipe integrity, particularly in the transition to a continuous water supply. The World Bank funded a laboratory investigation to assess in a controlled environment the causes of the harmful consequences and the remedies that can be introduced to alleviate their impact. This study is of importance not only in preserving existing networks in the transition to a continuous supply situation but also in ensuring that the large sums being invested in new infrastructure will not be wasted. Key Points: Transition from intermittent to continuous water supply of water distribution systems could be unachievableA laboratory investigation of effects and remedies that can be introduced to mitigate the impacts of intermittent water supply is presentedAir release valve design and location and control of the upstream conditions are crucial and must be properly analyzed [ABSTRACT FROM AUTHOR]

The evaluation of the impact of intermittent water supply on water distribution systems is a complex task. Laboratory tests, in controlled conditions with virtually no constraints on instrument and device location, allow the analysis of the effects of single parameters on pressures and flows. Within the framework of a research consultancy commissioned by the World Bank, the test network at the Water Engineering Laboratory of the University of Perugia, Italy, was modified to analyse pipe filling and emptying phenomena. Herein we describe the characteristics of the set-up, the available instruments and data acquisition system, as well as the installed devices (e.g., air release and in- and off-line ball valves). The set-up was also designed to investigate the effects of the air flow on the overbilling of water meters. The results of a preliminary test allow the typical phases of the phenomenon to be analysed, including the filling of the pipe with water and the discharging of air, the arrival of the water front at the downstream end causing a pressure variation typical of water hammer, and the emptying process and the filling with air. The analysis allows the operational mechanism to be understood and remedial interventions designed and validated. [ABSTRACT FROM AUTHOR]