Water Journal : Water Journal December 2012
non-revenue water refereed paper technical features 96 DECEMBER 2012 water meters. The second seeks to quantify how prevalent ‘low-flow events’ are in daily household water use. The third component considers the role that usage has on the Qs and, hence, the non-registration volume. These three pieces of information are then used to estimate non-revenue water attributable to non-registration (rather than under-registration) and are discussed in the next sub-sections. Meter testing at low flows Using a device called an Unmeasured- Flow Reducer (UFR) a study was conducted to show that non-registration below 5L/hr is apparent (CIEM, 2011a). The UFR is designed to reduce the amount of water that flows below the flow meter measurement threshold by changing the flow regime through the meter at low flow rates. For the standard new meter used in this study, the Qs (i.e ., minimum flow rate) was specified as 2L/hr (or 0.033L/min). Theoretically, therefore, water with a flow rate less than the Qs flow rate of a meter cannot be measured. Figure 2 details the flow rate recording accuracy for the new Qs = 2L/hr water meter, pre- and post-implementation of a UFR device. A summary of key findings from the study (CIEM, 2011a) are detailed below and are shown in column C of Table 1: • The new water meter (DN20) demonstrated a poor water recording accuracy less than 3L/hr. • The new water meter displayed accurate measurement after 6L/hr, with or without installation of UFR. • For flow rates from 0–2L/hr, there were significant under-registration of flows without the UFR, with only 14% and 36% recorded from flow rates of 0–1L/hr and 1–2L/hr, respectively; whereas, with the UFR, the measured flows improved to 55% and 85% respectively, indicating that measurement in these lower flow rate intervals improved with the UFR by 41% and 49%. • From 2–3L/hr, with the UFR, there was almost 95% flow recording accuracy, compared to 61% without the UFR (i.e. 33% more accurate than without UFR); • From 3–6L/hr, the meter with UFR was considered accurate. The UFR contributed to 5%–11% improvement in the measurement recording accuracy of the new meter. • The reason for some degree of non- or under-registration at these very low flow rate levels when using the UFR could not be established. • Based on the recorded accuracy with and without UFR, the average accuracy for flows recorded below 5L/hr was 57%. This inaccuracy was attributed to non-registration. This phase of the research gave an estimation of the magnitude of non- registration. The next section explores how prevalent low flow rates are, which could give rise to significant non- registered volumes. Consumption flow rate profile: prevalence of low-flow events Smart meters enable high-resolution flow data to be captured remotely and used for a range of urban water planning purposes (Stewart et al., 2010) such as demand management (Willis et al., 2010; Willis et al., 2011a), scheme evaluation (Willis et al., 2011b; Talebpour et al., 2011) and demand forecasting (Makki et al., 2011). To determine how often low flow events occur in a day, data was analysed from a sample of smart meters drawn from the South-East Queensland and Melbourne regions. High-resolution smart metering technology (i.e. 0 .014L/pulse at 5-second intervals) enabled flow data from over 400 households to be classified into the flow rate categories shown in Figure 3. The results are summarised as follows (CIEM, 2011b): • The first 11 flow rate categories shown in Figure 3 (i.e ., from ≤ 5L/hr up to the 91–100L/hr category) generally showed low flow events. Sources include leaks, internal taps, toilets, dishwashers, and some part of shower and clothes- washer events. Data collection does not include volumes of consumption in flow rates less than 2L/hr, as the minimum registration of a new meter is 2L/hr in Table 1. Non-registered water for a new meter as a percentage of the daily consumption. Interval category (L/hr) Flow rate interval (L/hr) Percentage of daily consumption per category (%) Proportion of interval volume in each category Recording accuracy of meter per interval Non- registered water per interval (%) A B C D=A*B*(1/C -1) 0≤5 0to1 1.31 0.05 0.15 0.37 1to2 0.12 0.35 0.30 2to3 0.23 0.60 0.20 3to4 0.30 0.85 0.08 4to5 0.30 0.90 0.04 5≤10 5to6 1.29 0.20 0.95 0.01 6to7 0.20 1.00 0.00 7to8 0.20 1.00 0.00 8to9 0.20 1.00 0.00 9to10 0.20 1.00 0.00 Total percentage non-registered water for a new meter 1.00 Figure 2. Flow rate registration accuracy for new meter with and without UFR.
Water Journal February 2013
Water Journal November 2012-1