Detection, Metering, and Audits
Metro Water Services uses three-pronged approach to recover non-revenue water
- By James E. Fisher
- Aug 01, 2007
“A lot of people think non-revenue water reduction is all about the leakage, but it isn’t,” says Leanne Scott, senior project engineer at Metro Water Services (MWS) in Nashville, Tenn. “Meter accuracy at large plants also plays a very important role in the recovery of non-revenue water, as does testing of other large meters in the system."
Almost all potable water systems have some amount of water that is produced but not sold or accounted for in other ways. This is commonly called “unaccounted-for water” or “non-revenue water” (NRW).
MWS, which monitors 2,800 miles if water pipeline, has performed leak detection since 1992 using in-house staff. The utility also has implemented water audits to help identify and recover NRW. Water audits help utilities obtain objective information about where the greatest amount of water can be recovered using the smallest amount of resources.
Because of the hilly terrain in Nashville, MWS has many water pressure issues (approximately 70 pressure zones) in its distribution system. The utility has had several leak survey programs using different contractors and consulting firms over the last 15 years, but it has consistently tried to reduce leaks and eliminate NRW.
When MWS performed its own leak detection, water losses increased because program surveyors also had to respond to customer issues. This shortage of manpower led the utility to seek a contractor in 1999. MSW initiated an RFP for an Unaccounted for Water Loss Program which evaluated experience, cost, small business participation, and business plan. The utility selected ADS Environmental Services of Huntsville, Ala., to conduct the three-year leak detection program. Its eight-year track record of success in performing work for Nashville’s wastewater system gave the company some advantage, Scott said.
Over the course of the program, the contractor found
• 672 leaks resulting in 9.48 million gallons per day (mgd) of water loss in the first two years, and
• 306 leaks resulting in 4.82 mgd of water loss in the third year.
Non-revenue water can be costly expense
The cost of producing the water from the plant to the customer (primarily chemical and electrical costs) is $0.25 per thousand gallons. This water savings amounts to $2.6 million for the three-year total of 14.3 mgd. Additionally, if 100 percent of this water was sold, it had a retail value of $37.4 million in the first two years and $37.6 million for the third year, based on current water and sewer rate structure.
The monetary value of non-revenue water also underlies the importance of including meter testing in a comprehensive NRW recovery program. It is standard policy of any city for all water lost through improper metering to be valued at the average retail price of water.
Two kinds of meters can be found in service at most utilities: production meters and customer meters. Each type of meter has its own type of test. Production meter tests validate water production data and are conducted by inserting a measuring instrument in series with the meter and comparing the rate of flow indicated by the instrument with the rate of flow indicated by the production meter. Procedures for customer meter accuracy tests depend on meter size. Larger meters are tested in place according to the American Water Works Association recommendations using calibrated test meters or by comparison with an instrument for large flow rates above the capability of a comparative meter testing unit.
Contractors and surveyors use sonic detection equipment to find leaks. The total length of water mains can be surveyed by placing the device directly on all hydrants and on numerous valves and services. MSW continues to work with contractors to perform their leak detection today.
Another critical aspect of a strong NRW recovery program is the water audit. In addition to the meter testing and leak detection being conducted in the utility over the past 15 years, MWS contracted for water audits for the past three years.
“The water audit is another critical element in gaining a comprehensive view of the entire water system,” says Scott. “It provides an independent look at the billing system, production, and distribution areas of the water process, some of which we had not examined until we did the water audits.”
MWS is converting to an automatic meter reading program and used information from the water audit to help prioritize which areas to address with the program. The new water meters supplied more accurate recordings of customer water use, removing meter error as a cause of water loss and easing the identification of leaking pressure zones. The audit showed the coding and other issues with billing that prevented MWS from communicating the correct numbers. The utility conducted an independent look and evaluation of the billing system to ensure the proper accounts were included in its analysis.
“As water becomes a more precious commodity, legislation and regulations are being enacted in many states to help preserve it. Many utilities already conduct water audits,” explains Cyrus Toosi, assistant director and chief engineer of Metro Water Services. “Water audits are critical and are the best way to be in control of non-revenue water. Ultimately, they will probably be federally required for all utilities.”
“Another benefit of removing as much non-revenue water as possible, particularly the real losses, is the possibility of deferring capital projects intended for growth,” says Toosi. “We have done both our Master Water and Sewer Plans in house, and we have recently been able to defer some of the projects because we have recovered real losses in key areas of our water distribution system”.
As they age, water distribution systems lose their efficiency for delivering treated water to paying customers. AWWA identifies two categories of NRW: apparent losses and real losses. Apparent losses occur because of inaccuracies in metering and billing systems while real losses result from the escape of drinking water from the distribution system. In efficient systems, NRW is less than 10 percent of the total. In inefficient systems, this percentage can exceed 20 percent and has been found as high as 50 percent in the worst systems. MSW now has about 20 percent non-revenue water; a few years the loss was greater than 30 percent.
The cost of facilities construction, treatment, and pumping of increasingly scarce water makes it economical to recover as much non-revenue water as possible. With average U.S. water rates nearly $2.50 per 1,000 gallons and rising, the return on investment for recovering 10 percent or more of a system’s total supplied water is great. Increased revenue by the water utility means more funds for other worthwhile projects and a lessening of pressure to increase user rates. For example, a system serving more than 100,000 customers may produce 79 mgd. If this city’s non-revenue water percentage is at 20 percent, then nearly 16 mgd is not billed. This loss has a market value of $40,000 for each day that the problem goes uncorrected.
Real losses represent a waste of increasingly scarce potable water. Recovery programs can reasonably be expected to recover around half of the lost water, although that percentage will vary widely from system to system.
MWS has been progressive in its approach to addressing NRW, beginning to address water loss as far back as 1946. Many other water utilities in the United States will be forced to address these losses either due to water shortages, legislative action in the near future, or good stewardship of water utility for future generations.
This article originally appeared in the 08/01/2007 issue of Environmental Protection.