(Published by Water Utility Infrastructure Management (UIM), September/October 2012)
By Matt Thomas, Mueller Systems
Non Revenue Water (NRW)—the difference between the volume of water supplied to a water system and the volume of water billed to customers—is a critical issue for water utilities. According to World Bank estimates, NRW has an estimated value of more than $18 billion per year worldwide. This figure represents treatment and distribution costs and the missed billing revenues of water that is “lost” through the system before it reaches customers.
NRW is caused by a combination of apparent losses (meter error, under-estimation of meter reads, incorrect size/types of water meters, bypassed meters, use from unmetered fire lines and theft), unbilled authorized consumption (hydrant flushing, community pools, parks and firefighting) and real losses (leakage from transmission and distribution lines, storage tank overflows, couplings, customer meter leaks, and unavoidable leakage).
Fortunately, technological advancements have resulted in tools that can help water utilities better manage NRW. Two-way advanced metering infrastructure (AMI) is an example of such a development that can provide utilities with information to help them better account for NRW by ensuring optimal metering accuracy, identifying potential leak zones and identifying the extent of their NRW problem.
Optimal Metering Accuracy
Using the correct size and type of meter for each connection is important for a utility to accurately account for water distributed through its system. Typically, meters are most accurate when operated in the “normal” or “intermediate” flow rates published by the manufacturer.
Many of today’s water meters are oversized and lose revenue from leaks and low flow. In general, the larger the meter size, the less accurate it is at low flow rates. Notwithstanding this fact, we see utilities increasing the size of residential meters from 5/8” to 3/4” and even to 1”. These changes can lead to increased NRW because of reduced fixture values (i.e. toilets 5 gpf to 1.6 gpf) and other conservation initiatives that show a declining residential use.
Utilities too often base the sizes and types of water meters they use on pipe size rather than flow rate. Not only can this negatively affect accuracy, it can also reduce the life-span of meters if they are used in scenarios where flow rates regularly exceed half of their operational capacities.
Utilities should base their metering size/type decisions on current fixture values and confirm the data with the lowest/highest hourly average flow rate during usage.
Calculations should be made according to peak and low flows over a period of at least 30 days, in hourly (or even 15 minute) increments to properly determine water use. Utilities can leverage AMI to accurately calculate these flow rates for each specific account.
Instead of basing flow rates on consumption data that is collected only once a month and provides limited insight regarding high and low consumption rates, utilities can use 15 minute, hourly, daily or weekly consumption data stored by AMI components and uploaded to databases in their servers. Once the required low/high flow rate is calculated, it can be compared to the operational capacity of the best type/size of meter.
If the hourly low flow rate is found to be below the meter’s normal operating capacity, the utility would then know that the meter is oversized for the particular account and its accuracy may be questioned. Under such circumstances, it would be advisable to replace the meter with one of a different type and size that would be better suited for measuring the volume of water used by the account.
Not only can this information help utilities improve billing accuracy, it can prevent them from needlessly spending money on larger, more expensive meters.
Identification of Leak Zones
In addition to more effectively determining metering accuracy, utilities can use information provided by AMI systems to help identify leak zones that may be responsible for NRW losses. Identifying leak zones can enable utilities to more efficiently prioritize repair projects or add leak loggers for areas that have the highest potential for water loss.
A key component of leak zone identification is establishing district metering areas or “DMAs.” A traditional DMA is a defined area of the distribution system that can be isolated by meters or valves. Through AMI, DMAs can now be created with technology; a utility can retrieve readings from a large number of a particular zone’s meters (master meters, permanent or temporary) as well as readings that are simultaneously stored by all of the residential or commercial meters located in the DMA.
By analyzing the flow and pressure of a particular DMA, especially at night when a high proportion of users are inactive, utilities can calculate the level of discrepancy between the amounts of water going in and out of the DMA. The level of difference between these two amounts can alert the utility to the extent of potential leaks in the area.
A comparison of the levels of potential leakage among different DMAs will allow the utility to prioritize maintenance projects that will have the greatest impact in terms of reducing NRW losses.
Overall Extent of NRW
AMI can also serve as a tool to help utilities determine the overall extent of their NRW problem.
AMI systems are configured to fully automate the meter reading-to-billing process, linking meters, distribution sites and control devices in a single data network. Their major components work together to completely automate the process of accurately determining how much water a customer uses for any period of time.
A utility can request a real-time reading from all water meters in its system to account for the amount of water that it is being metered (or billed to customers) at any given time. The volume of water being metered can be subtracted from the total volume of water being purchased by the utility for distribution. The difference between these two numbers is the amount of water that is not being metered—or, the volume of NRW.
It should be noted, however, that cities typically use a certain amount of water that is seldom billed for municipal activities such as hydrant flushing, community pools, irrigation of city parks, firefighting, etc. With AMI and DMAs, it is becoming possible to accurately account for this unbilled authorized consumption, which can be factored to help utilities get an even better high-level view of how much revenue they are missing out on as a result of NRW.
Utilities’ ability to properly assess and control water losses to help ensure the efficient use and distribution of water resources to all legitimate customers is extremely important, as water consumption is expected to increase approximately 40% by 2025, according to the World Water Forum. Furthermore, utilities cannot afford the missed revenues and enormous costs of NRW, given the budget shortfalls many of them are facing.
By implementing AMI, utilities can access the level of information they need to better understand their water systems and effectively decide what measures to take in order to more accurately account for lost water.
Matt Thomas is Vice President of Marketing for Cleveland, NC-based Mueller Systems, where he helps water utilities increase water revenues, improve water conservation and lower operating expenses through proper metering technology. A long-standing member of the AWWA Water Meter Standards Committee, Thomas co-authored the recent AWWA M6 manual titled, “Water Meters – Selection, Installation, Testing and Maintenance”.