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Mathematical Solution for Average Metering Error of Domestic Water Meters - a Relative Error Method

As everyone knows that domestic water meters have metering errors which cause under registration in average. However almost no one can be sure what the figure is, because the metering error is affected by two complicated behaviors: water consumption of household, and the inaccuracy of meter itself. And it is hard to gain enough data for studying both of them.
Actually, the two behaviors are already contained within historical meter readings. This research analyzed the meter readings and developed a practical approach to identify average metering error for water utilities. Using the RM-z μ chart with the equations comprising statistical parameters, Taipei Water Department (TWD) has successfully estimated average metering error in its 99.6% domestic meters, including Sub Meters (-9.85% in average, under registration), Master Meters (-6.11% in average, under registration) and Direct Meters (-10% in average, under registration). Due to TWD’s specific billing mechanism among Master Meters & Sub Meters, the equivalent metering error of Master-Sub meter groupings is only -4.26% in average. And its metering performance is better than any other non-grouping meters. Additionally, this method may provide an alternative way to estimate the Customer Meter Inaccuracies term in Water Balance Sheet.