Water Journal : Water Journal December 2012
refereed paper non-revenue water water DECEMBER 2012 97 specification and potentially higher in practice, as illustrated above. Therefore, the 0 ≤ 5L/hr category essential has flow recorded in the 2 to 5L/hr range. • The middle flow rate range made up the majority of total water use (i.e., from 100L/hr to 1200L/hr), especially the 300–600L/hr interval. Sources include showers, clothes washers, irrigation and external taps. • The rest of the range (i.e., from 1200L/ hr to over 1800L/hr) can be attributed to showers, clothes washers, irrigation, external taps and uncommon water usage (e.g., service break leaks). The first three flow rate categories shown in Figure 3 are the most important for estimating non-registered volumes. Therefore, the following values were applied in conjunction with the above meter-testing results to provide a robust estimate for non-registered flow: • 0 ≤ 5 flow rate interval category: 1.31% of total residential consumption; • 5 ≤ 10 flow rate interval category: 1.29% of total residential consumption; and • 10 ≤ 20 flow rate interval category: 2.32% of total residential consumption. Impact of usage on non-registration It is well known that meter ageing, or more correctly meter usage, affects meter accuracy for flow rates above Qs (Arregui et al., 2005). To date, there has been little reported on the relationship between non-registration of meters (i.e. below Qs) and age due to the cost of this type of testing and, historically, a low level of concern for this type of water loss. The escalation of water tariffs in the past five years and a heightened expectation of better accounting of system input volumes has emphasised the need to provide sound estimates of citywide non-registration volumes. To address this knowledge gap a small sample of meters from across the three Melbourne urban water utilities’ jurisdictions, with differing registration volumes, were tested to determine their Qs (WBW, 2011). The meters were assembled in batches of three meters in series with similar usage registration. The worst case for each batch was recorded, i.e. the flow at which the last meter in the testing batch started to register water flow. Ideally, individual meter testing should be conducted to obtain a more accurate relationship between meter age and Qs instead of this adopted sampling approach; however, the testing time for each test (i.e. 6 –8 hours per test) and the rig’s limited availability for research testing activities, meant that this alternative testing approach had to be adopted. Nonetheless, the results and trend established would closely resemble that obtained if the ideal testing procedure was followed and individual meters were tested. The results are illustrated in Figure 4, where it can be seen that older meters (3000+ kL) exhibit a Qs that is more than double the Qs of a newly installed meter – i.e. 7 .26L/hr and 3.4L/hr respectively. Therefore, the decreasing accuracy of the meter not only results in under- registration of usage volume but also results in higher non-registration thresholds. As such, any estimation of non-registered water must take account of a region’s meter age and type profile. Understanding Components of Unregistered Water Determining under-registered volumes All meters have specified ranges of accuracy and must comply with the NMI R 49 specifications for maximum permissible error for domestic flow meters, as shown in Table 3 (NMI, 2009a). The under-registration of a fleet of meters is best determined by annual random sample testing of the fleet to take into account the specific network operating conditions, and the registered usage of the meters. To obtain the average error for a meter across a range of flows, the meters are tested against the flow rates shown in Table 4, and the errors weighted according to the flow profile (similar to the one shown in Figure 3) of an average domestic consumer. The first line of Table 5 provides the average percentage error in the meter registration for a representative sample from two Victorian water utilities of 660 20mm meters of the same brand and model. As can be observed, the results fall well within the NMI specifications. Also, the registration begins as an over- registration when the meter is relatively new and under-registers when the meter has registered greater than 2000kL. This result may vary from utility to utility and between brands and models. Calculating non-registered volumes This section combines the above empirical findings to develop an estimate of non- registered water in residential households. 0-<5 5-<10 10- <20 20- <30 30- <40 40- <50 50- <60 60- <70 70- <80 80- <90 90- <100 100 - <200 200 - <300 300 - <400 400 - <500 500 - <600 600 - <700 700 - <800 800 - <900 900 - <1000 1000 - <1100 1100 - <1200 1200 - <1300 1300 - <1400 1400 - <1500 1500 - <1600 1600 - <1700 1700 - <1800 > 1800 Prop of T Con(%) 1.31 1.29 2.32 1.49 0.7 0.64 0.57 0.66 0.67 0.55 0.6 4.99 8 .39 11.28 15.38 8.6 9 .01 7.14 6.17 6.43 2.89 2.9 1.3 0.92 0.67 0.51 0.43 0.26 1.92 Cum Prop of T Con(%) 1.31 2.6 4.92 6.41 7.11 7.75 8.32 8.98 9.65 10.2 10.8 15.79 24.18 35.46 50.84 59.44 68.45 75 .59 81.76 88.19 91.08 93.98 95.28 96.2 96.87 97.38 97.81 98.07 100.00 0 20 40 60 80 100 120 0 2 4 6 8 10 12 14 16 18 Cumulativeproportionoftotalconsumption(%)Proportionoftotalconsumption(%) Flow rate category (L/hr) Figure 3. Proportion and cumulative proportion of total water consumption (%) in each flow rate category (SEQ and Melbourne region combined sample, n = 406). Figure 4. Average starting flow rate (Qs) of tested meters.
Water Journal February 2013
Water Journal November 2012-1