Modelling consumers in intermittent water supplies: a comparative review of EPANET - based methods

Abstract

Intermittent Water Supply (IWS) networks, which pressurize for less than 24 hours/day, affect 1 billion people worldwide and are associated with increased water contamination and inequitable distribution. Due to these downsides, various methods to model consumers and understand their behaviour were proposed. We found more than 8 different methods of modelling IWS consumers, but we know of no comparative analyses of these methods nor their efficacy. This study comparatively reviews methods of modelling IWS consumers implemented in EPANET, due to their prevalence, reproducibility, and accessibility. Methods of modelling IWS consumers were found to fall into three groups based on their assumed consumer withdrawal behaviour: unrestricted, flow-restricted, and volume-restricted methods. We applied each method to three reference networks and compared the methods’ performance after subjecting each reference network to common IWS improvement strategies, including changing the supply duration and/or source pressure. Flow-restricted methods assume consumers withdraw their demands at a constant rate, leading to unrealistic predictions when subjected to unexpected changes in supply conditions. Volume-restricted methods assume consumers withdraw at the highest, hydraulically feasible rate until their storage tanks fill. This assumption highlights pronounced inequality between consumers, as consumers advantaged by source proximity and/or elevation receive their demands faster and earlier. Our results demonstrate that the simulated behaviour of IWS depends substantially on the type of consumer model employed. Presented examples demonstrate that consumer model selection can change the simulation-predicted optimal strategies for coping with and improving IWS. IWS modelling methods should reflect the consumer behaviour in the modelled network and the model’s intended use.