IWA Publishing

Case Studies Demonstrate the Implications of Metering Errors

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General anomalies that occur in the management of apparent losses are identified and include determination of apparent loss indicators that fail to take into account both the random and bias errors inherent in metering. Estimating the volume of water losses that could be attributed to meter errors is also incorrectly assumed to be equivalent to the error limits (i.e. envelope) stipulated in standards. Performance indicators that are reliant on flow meter data must be expressed as a range and not as a single value which is common practice. It is shown that the measurement error range decreases as the number of meters increase when combining both their bias and random errors. A default value for reference annual apparent losses (RAAL) is quoted as 5% of the authorised consumption unless historic records can demonstrate otherwise. This 5% value relates to water meter errors that are only one component of apparent loss contributing to a volumetric imbalance and still requires inclusion of random errors in its calculation and therefore should be reported in the form of a range. Meter measurement errors include those of the meter fleet (e.g. revenue meters) as well as large (bulk supply) meters.

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