Page 208 - Water Loss Control

182 Cha pte r T w e l v e

for residential use, and all other (larger) meters which include industrial, commercial,
agricultural, and meters for other applications. Testing can serve both the general pur-
pose of providing information to the water audit on the system-wide level of apparent
loss due to customer meter inaccuracy, and to identify the accuracy of individual meters,
thereby allowing meter improvements to be implemented where needed.
AWWA’s guidance manuals on meters give excellent instruction on meter accuracy
testing. These include the M22 publication and the M6 publication, Water Meters— Selection,
Installation, Testing, and Maintenance, the latter of which provides comprehensive informa-
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tion on the basics of customer meter management. Generally, accuracy tests should be
conducted at low, medium, and high flow rates. For small, residential meters sample
groups of meters can be tested. A randomly selected sample of several dozen to several
hundred meters (depending on the size of the meter population) can be selected and tested.
A separate sample of meters with high cumulative consumption should also be tested.
Results of the latter testing can help to develop a long-term meter change-out strategy
based upon the level of cumulative consumption at which accuracy begins to decline.
Because there are hundreds or thousands of customer meters in a drinking water
utility, it is impractical to inspect and test every one each year. Instead, the water utility
manager can identify sample numbers of customer meters of various sizes and types
for inspection and testing. The results of such sample tests give a reasonable indication
of the status of the entire customer meter population.
Residential (small) meter testing: Many utilities operate meter testing and rotation
programs. Particularly for small meters, it has become more cost-effective to replace
meters than to repair them. Random or specific testing to determine the accuracy of
installed customer meters can be conducted to monitor the wear of meters. A represen-
tative sample of newly purchased residential meters should also be tested to confirm
the acceptability of the newly delivered meters. All of this test data represents a good
source of information to infer the overall degree of inaccuracy existing in the customer
meter population. In this way the level of apparent loss in the system can be quantified
for the water audit. Test a random sample of residential meters, 50 to 100 is a sufficient
number, but the optimal number to be tested depends upon the size of the customer
meter population, the degree of confidence required in the test results, and the variance
in the actual test results observed. Residential meters may be tested on a test bench or
sent to the factory or a testing service contractor for testing.
Tables 12.3 to 12.5 give an example of calculations using small meter accuracy test
data to determine the level of apparent loss from small meter inaccuracy included in the
water audit for County Water Company (AWWA 2008). Weighting factors for small
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meter flow rates are given in Table 12.3. The weighting factors reflect common percent-
ages of time that flows are found in the low, medium, and high flow ranges, respec-
tively, with flows existing most often in the medium range for most properly sized
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meters. In the example 50 randomly selected residential meters are tested for low,
medium, and high flows with summary test results shown in Table 12.4. These results,
shown as a percentage of accuracy, are used to calculate the total meter error at average
flow rates. Table 12.5 demonstrates how to use existing meter test data to calculate total
residential meter error. The resulting residential (small) meter error for County Water
Company is given at the bottom of Table 12.5 as a value of 134.33 million gal for calen-
dar year 2006.
Industrial/commercial (large) meter testing: Large industrial, commercial, and agricul-
tural meters register a much greater portion of consumption and produce a much larger
share of revenue per account than do residential meters. For many water utilities over