Characterising the unequal supply of water in an intermittent water supply network in Lahan, Nepal

Daily pressure traces used to calculate the median supply hours across the piped network. Intermittent water supply (IWS) affects over one billion people worldwide, resulting in unequal delivery of piped drinking water. Limited data from operational networks constrain our understanding of the processes driving this inequality. This study utilised 12 pressure loggers, measuring at 15-min intervals over 30 days, to reveal the spatio-temporal pressure distribution across multiple supply cycles in an operational IWS network in Lahan, Nepal. A new statistical method for defining supply hours was developed to characterise highly variable supply conditions, deconstructing the monolithic concept of ‘supply hours’. Comparison with other network parameters identified key physical drivers of supply inequality: distance from the nearest source governed the duration of ‘high-pressure’ supply hours, while network elevation drove ‘low-pressure’ supply hours. The study provides new evidence of the importance of the draining phase in IWS cycles, showing that in this network, the lowest elevations receive continuous supply due to localised water pooling. Finally, the findings highlight challenges in designing network improvements; interventions such as network zoning could inadvertently reduce supply hours in certain locations. Network managers must therefore account for localised conditions to avoid negatively impacting water access for vulnerable consumers.