By David Allen, P. Eng.*
*Product Manager, Schlumberger Measurement Division
The water industry is now experiencing what the business sector experienced 20 years ago: an explosion in the use of computers. This situation is giving utilities the chance to address almost any problem or application.
The new technology includes systems that increase and improve the management of revenues by monitoring, recording, storing and analyzing data from water meter use patterns. This process is called "flow profiling", and it enhances the operation of a utility's "cash registers" or water meters by:
Previous approaches (such as chart-recorders, telemetry, and SCADA systems) for analyzing meter data generally have provided limited information or have been too expensive for the average utility.
By adopting a flow-profile system, many utilities are now reclaiming revenues they would otherwise be losing for many reasons, ranging from billing disputes to improperly sized meters.
Typically, the profiling system consists of a recorder, transmitter (for sending meter data to the recorder), and PC software. To conduct a flow profile, the recorder is programmed for the length of time it is to be in the field. Then it and the transmitter are retrofitted onto the flow meter. Once the profiling is complete, the data can be retrieved by:
The DTU is used for collecting multiple profiles. User-friendly software, with pull-down menus that export data to spreadsheet software programs for presentation in graphical or tabular reports simplifies system use.
Solving application problems
Depending on the application, one or more utility departments can benefit by conducting flow profiles on water meters. These departments include customer service, metering, distribution, finance, water conservation, and even engineering. The typical problems that utilities are confronting include:
Water theft: Water theft occurs in a variety of forms, from tampering with water meters to tapping unmetered fire lines. Fire lines without meters are typically installed with a detector check valve and a by-pass meter, but they do not indicate the amount of water used, only that consumption has occurred. Whether on purpose or by accident, such use, besides costing money, poses a considerable threat to the potable-water supply because the connection has no backflow preventer.
The customer suspected of stealing water likely will attribute the loss to leaks, unless the utility has flow-profiled documentation of theft. For example, documentation showing consistent use between midnight and 6:00 AM might indicate that the water is being used for a third-shift operation. If theft is occurring, an appropriate meter can be installed to record all water used by the end user.
Leaks: Leaks are among the major factors contributing to unaccounted-for water. They can be detected by monitoring flows and consumptions at a distribution master meter and subtracting the consumption registered by the end-user or billing meters in a specific area. The difference represents a water loss due to leaks; or else, the meters are inaccurate.
Also, an abnormally high use profile during off-peak consumption periods indicates a leak. A test done at a Toronto area brewery showed a 30 gpm consistent flow during the night when no production was taking place.
Besides their economic costs, undetected leaks can create counter-productive customer relations. A customer with an undetected fixture leak (toilet, faucet, or lawn-sprinkler head) usually surmises one reason for an unusually high water bill: a faulty meter. The customer, provoked by the high bill into being tough-minded, will contact the utility, claiming not to have used "that much!" water. Where the utility cannot get the customer to pay the high water bill, that revenue may have to be written off as a bad debt (adding to the unaccounted-for water rate).
By profiling the customer's use pattern (that is, by documenting the leak), the utility can prove that a leak, and not a faulty meter, is causing the high water use. The outcome is better customer/utility relations and a better basis for collecting the revenue. In addition, the utility saves the time and trouble of changing out the meter to prove it is not at fault.
Correct meter sizing
Oversized or inaccurate meters contribute to the unaccounted-for water not attributable to leaks or theft.
Large meters routinely make up one percent of the meters in a system, but account for 60 percent of many utilities' revenue. Obviously, to maximize revenue, it is important that the large meters be maintained for accuracy. Accuracy, in large part, can be ensured by sizing and applying meters correctly; and correct sizing can be ensured by flow-profiling.
Almost every system has its share of oversized large-diameter water meters. Oversizing occurs when replacing meters without regularly re-evaluating the customer's use pattern. A manufacturing process that requires large volumes of water may have been discontinued.
Where the installation consists of a 4" turbine water meter installed in a 4" line, typically a new 4" turbine meter will replace it. The utility rarely resizes the meter to match the consumer's use patterns. Apparently, utility managers often neglect to consider that, over time, end-user consumption patterns also can change. Where the 4" meter was once required, a 1 1/2" meter may be adequate now.
Maintenance procedures require an accuracy test at specific flow rates as per the AWWA M.6 manual. Although the meter may be accurate at the flow ranges being tested, in actual conditions, water volume passing through the meter may be well below these ranges. The result is an inaccurately registered water flow.
For correctly sized meters, the maximum continuous flow should not exceed 50 percent of the meter's flow capacity. In addition, no more than 5 percent of the flow should occur below the meter's minimum flow rating.
Compound meters must meet yet another proper size criterion; 80 percent of the total flow should pass through the turbine side, and 20 percent should pass through the disc side. Ratios other than this indicate a problem of over or undersizing.
Meter replacement programs
Utility managements often do a payback analysis when they consider changing out old or inaccurate water meters. New meters, by capturing lost revenue can ultimately pay for their purchase. The payback time (break-even point) depends on the amount of the extra income that the new meters earn. If the extra earnings per meter are $X per year and the cost to buy and install it is $Y, then the break-even point is Y/X years. Lost sewage revenue also should be considered, since sewage revenue directly depends on the accuracy of the meter.
Lost revenue is a direct function of meter inaccuracy. Therefore, calculating the break-even point requires knowing the meter's (in)accuracy. Historically, management has used an accuracy-averaging method for this analysis. This consists of testing meter accuracy at the low/intermediate and full-flow ranges. The results of these accuracy tests are then added and divided by three. The tests, however, fail to account for the slight bell shape of the meter accuracy curves. As a result, tested accuracies may be deceptively high. The method consequently tends to yield overly-conservative payback periods, which may discourage utilities from changing out meters even as they continue to lose revenue.
The data from flow profiling gives the correct payback period because it provides true accuracy averages for each flow range. It also provides an actual distribution of flows within the three meter ranges, These two data sets can be used to calculate the real accuracy profile of the meter as it is being used in the specific application.
| Table 1 - Meter use as it depends on meter type | |
| Type | Application |
| Positive Displacement | Low-to-moderate flows (nutating disc), residential, light commercial |
| Turbine | Consistent moderately high flows; commercial, industrial |
| Compound | Large fluctuations (from low to high flows) |
Other benefits
Water-use analysis of flow-profiled data can help with a variety of other application problems, including:
Proper meter-type: The three most common types of meters used today and their applications are shown in Table 1. Given this choice, utility managements sometimes have problems, without accurate profiling data, selecting the right type of meter for the right application.
Demand metering: Billing large consumers by time-of-use or demand metering based on flow-profile data can quickly and potently affect water-conservation efforts. It can also:
Peak-use analysis: Peak-use analyses have wide application and are typically used to:
This data can be used to justify the expansion of distribution lines or to address low-water-flow or pressure problems.