Combatting reduced recovery rates based on water meter degradation - by Nicole Paul

March 19, 2019 - Spotlights
Nicole Paul,
Energy Management
Systems, Inc.

Water meter degradation can be defined as the need to replace existing water meters with new meters due to under-reporting of actual tenant consumption and lower flow rates associated with the meter types aging. Rapid amortization of the investment is based on the advanced age of the target water meters and the propensity for older meters to degrade over time. Studies date back to 1987 by G.J, Newman, when the water utility industry began to document the susceptibility for older water meters to suffer degraded accuracy and under-reporting of actual consumption. (Optimal Testing Frequency for Domestic Water Meters, Noss, R.R.; Newman, G.J.; & Male, J.W.) 

Water meters are not able to exactly register the total amount of water consumed since they have a limited range of operation. Its performance normally diminishes at low flow rates, which are in most cases due to leaks in the user’s facilities. (Key Factors Affecting Water Meter Accuracy, Arregui, F.; Cabrera, E.; Cobacho, R.; & Garcia-Serra, J.) This problem increases with water meters aging since the accuracy curve decays over time. For instance, a study done by the Water Engineering and Management Journal, explains that meter accuracy degrades rapidly on average after 20 years, falling from a real meter accuracy of 99% down to 82% by year 30. (WEMJ, Allender, Hans, Dr.) In addition, the size of the meter in relation to aggregate flow-through volume can cause problems, as smaller meters with low flow rates result in the highest degrees of inaccuracy. (The Water Research Foundation) 

There are three specific factors to focus on when analyzing meter degradation and the reasoning for this occurring: Age, rate of degradation and low flow rates. Accuracy degradation only in low flow scenarios for a 20-year-old meter according to Dr. Allender, may be as high as 40% degradation or the meter may be only 60% accurate. (WEMJ, Allender, Hans, Dr.) In addition, there is also the issue of renewing the meters too often that will produce economical losses caused by the fixed costs of the investment. To solve this issue, you must either test every single water meter in the system, to exactly determine the average performance at different flow rates which can be costly or rely on statistically representative samples of each type of meter. It is also important to determine water meter weighted accuracy with the average water consumption pattern, which gives information about how much water is used at different flow ranges. The weighted accuracy is the parameter used to estimate the total unmetered water volume over time and the optimal replacement frequency of meters (Davis, S.E., Residential Water Meter Replacement Economics). 

One excellent example of water meter degradation would be when EMS replaced the water meter set at a property for a national REIT. The national REIT water meters were experiencing exceptional recovery rates in the two months after meter replacement and exceeded the two months prior to meter replacement by an outstanding 37%! This example further reinforces the idea that water meter degradation occurs and that there are benefits in cost recovery when the meters are replaced. In addition, it supports the assertion that this national REIT has an opportunity to greatly increase its recoveries through water meter replacement, in addition to the operational benefits of a conversion to full AMR readings. In conclusion, building owners should pay close attention to the age of their meter, and get them replaced with new meter equipment or read with AMR to avoid inaccuracy of meter reads and tenant consumption later down the line.

References: 
Allender, Hans, Dr. Determining the Economic Optimal Life of Residential Water Meters, Water Engineering and Management Journal, 1996
Arregui, Cabrera; Cobacho, R.; and Garcia-Serra, J., 2005. Key Factors Affecting Water Meter Accuracy. Proc. Leakage 2005
Davis, S.E., Residential Water Meter Replacement Economics, Leakage 2005 Conference Proceedings, 2005

1 In 2001, the Water Research Foundation published the results of an extensive four year a research study, “Accuracy of In-Service Water Meters at Low and High Flow Rates” 
2 Noss, R.R.; Newman, G.J.; and Male, J.W., 1987. Optimal Testing Frequency for Domestic Water Meters. Journal Water Resources Planning & Management Div.— ASCE. 113:1:1.

Nicole Paul is a marketing communication specialist at Energy Management Systems, Inc., Exton, PA.

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