Determination of water meter performance under different pressures and intermittent supply

Abstract

Non-Revenue Water (NRW) at 35% in Kampala Water and National Water and Sewerage Corporation (NWSC) is above the recommended minimum NRW figure of 25% hence the need to tame it lower. In Africa water supply systems operate with varying pressures for example in south Africa it ranges from 6 to 2 bars (trijdom, 2016), 2 to 7 bars in Nigeria, Kampala’s average pressure ranges from 7 to 1 bar and some places with intermittent supply falling below 1 bar at the customers’ water meter . This study was aimed at determining the meter accuracy degradation profiles in the different pressure and supply zones of the Kampala water distribution Network (KWDN). The National Water and Sewerage Corporation (NWSC) is charged with ensuring provision of safe potable water to the population of Kampala. Under this study, water meters were classified according to the three pressure zones i.e. Low, Medium and High and the supply zones (intermittent and continuous) in the KWDN. The NWSC meter laboratory test data of four years (2016-2019) from each pressure and supply zone was collected and analyzed to develop models between meter accuracy and pressure as well as intermittent/continuous supply. The comparative meter accuracy analysis methodology which uses pressure/supply status, meter accuracy and totalized volume data was utilized. Regression analysis techniques were later applied to investigate the effect of pressure and supply status on meter degradation. Three non-linear degradation models that consider meter accuracy and totalized volume have been developed for each of the three-meter types from the test results. The results showed that water meters exhibited different deterioration models across the different pressure and supply zones (deterioration of water meters was highest in the low-pressure zone followed by the high-pressure zone and lowest in the medium pressure zone). For example, model 2 meters at a totalized volume of 3000m3, showed accuracies of 75.4%, 88.8% and 91.4% in the Low, high and medium pressure zones respectively. Single jet water meters (meter model 3) generally have a lower degradation rate compared to multi jet water meters. This study shows that generally water meter accuracy degrades faster (up to twice as much) in intermittent than in continuous supply zones. This study therefore recommends that the choice of water meters should be based on operational pressures and supply status of a water distribution network and discourages generalising meter deterioration over time without looking at pressures. Keywords: Degradation profiles, pressure zone, water meter accuracy, water meter’s deterioration