Page 213 - Water Loss Control

186 Cha pte r T w e l v e

Total Volume at Meter
Sales Flow Rate Meter Error
Percent Volume † (Vf) Registration Meter Error (ME) (ME)
Volume ∗ (Vt) (%V ë Vt) (R) ‡ ME = Vf/(0.01R) - Vf million
(%V) million gal million gal percent million gal gal
10 939.2 93.92 90.0 [(93.92/0.90) – 93.92] 10.43
65 939.2 610.48 96.54 [(610.48/0.9654) – 610.48] 21.86
25 939.2 234.80 101.0 [(234.80/1.01) – 234.80] −2.32
Total Meter error for large meters (line 19)……………………………………………… 29.97

∗ From Table 12.6.
† From Table 12.2 sum of industrial, commercial, and agricultural metered consumption.
‡ From Table 12.7.
Source: Ref. 1
TABLE 12.8 Calculation of Large Water Meter Error

the utility to keep statistics on accuracy levels versus the cumulative volume of water
registered for various brands and sizes of meters. Conversely, complicated logistics
usually require large meter accuracy to be carried out at the customer location. Due to
the significant portion of water consumption billings that are generated by large cus-
tomer meters, a formal large meter-testing program is recommended for the water util-
ity maintenance program. Many water utilities have published accounts documenting
that increased revenue and water accountability gains have substantially offset the ini-
tial investment and continuing costs of such testing programs.
It is important to keep detailed records of meter account histories and accuracy test
results obtained at the various flow rates. For an on-site test, remember to record the
meter’s registration before and after the testing so the customer is not charged for the
water used during the test.
As discussed in Sec. 12.3, meter accuracy test results and the water rates charged to
customers are needed to determine the target meter replacement rate based upon even-
tual drop in accuracy from high cumulative flows passed through the meter. Each util-
ity should attempt to establish the level of inaccuracy—and commensurate cumulative
volume—that prescribes when meters should be repaired or replaced. In order to obtain
sufficient data to determine the economic target, a reasonable number of randomly
selected and high cumulative volume meters should be selected for testing each year.

The Customer Meter Accuracy Testing Methodology
Meter accuracy testing can be performed on-site at the customer premise or at a testing
facility. When testing meters on-site, the methodology is to compare the accuracy of the
meter being tested with a calibrated meter tester used in the process. The calibrated
meter has its own performance characteristics and is not 100% accurate across its entire
flow range and should have an available compensation curve describing this. Meter
accuracy tests conducted at a test facility usually offer better validated results since the
volume of water passed through the meter(s) being tested flows into a tank of known
volume. Therefore the test process is well calibrated, since the volume passed through
the meter is known precisely. Photos of the large and small meter test benches of a
typical water utility are given in Figs. 12.7 and 12.8.