Distribution System Leak Detection (Water Loss)
This conservation consists of two possible components:
- Leak detection
- Leak repair
Leak detection is the process of searching for and finding leaks in the system with sonic, visual, or other indicators. Reviewers have noted that sonic and acoustic leak detection equipment is more accurate for smaller systems than for larger systems. Audits and detection programs incur costs whether or not repairs are made; thus, audits and detection alone do not save water. Conversely, leaks are sometimes discovered without organized audit and detection programs. Finally, reviewers have noted that ”leak prevention” would also be part of these programs, including corrosion control, quality control on materials and installations, and backflow device testing. Kunkel and Beecher (2001) and Flowers (2001) review the challenges of defining water loss in a way that makes reporting meaningful.
Farley and Trow (2003, source book) and Trow and Farely (2003, summary paper) provide a comprehensive overview of the IWA approach to leakage management in water distribution systems.
BMP 3 – System Water Audits, Leak Detection and Repair calls for prescreening audits, full-scale audits when indicated, and repairs.
Available Water Savings Estimates
Summary of Individual Studies
The incremental savings of leak detection are the additional savings from repairs that: a) would not have taken place without the program or b) would have taken place at a later time and perhaps more severely. Moyer (1985) makes the rough assumption that leaks are detected one year earlier than they would have been without the program. Thorton (2002) contains case studies, which report savings and costs for a number of programs conducted in the field. For example, the Moyer et al. (1983) study below is summarized in the Thorton text.
Moyer et al. (1983) report the results of six years of leak detection and repair activities at the Westchester Joint Water Works in Mamaroneck, New York as follows: 498 leaks detected, or 10,469 ML water saved, and $239,062 total leak detection and repair costs.
Young (as published in Thorton, 2002), found savings of 1,110 cubic meters using advanced water pressure management in a Johannesburg, South Africa. Maddaus, Arsdel, and Woody (2004) report the total system water loss in the Asheville, North Carolina service area was 36 percent for year 2002. Among other results reported, 61 large meters were tested and it was found that 10 meters were un-testable, 16 meters failed, and 35 meters passed. Preliminary results show a 46 percent fail rate for small meters between 5/8” and 1”.
Lalonde (2004) reports savings of 6.5 percent on average resulting from pressure management strategies that reduce pressure, on average, 14psi. Thorton (2004) reports savings from one case study (York Region, Toronto, Canada) of 1.57 million gallons per day, equating to a 22 percent savings of the original non-revenue water. A second case study regarding Irvine Ranch Water District single-family residential pressure reduction found 1.9 percent savings and 4.1 percent for those with large landscapes. A third in Sao Paolo, Brazil project annual savings of 671 million cubic meters resulting from installation of pressure stations, increased leak detection and response time, small revenue meter change-outs, large meter change-outs, meter resetting, recovered physical loss, and recovered non physical loss. Bardsley and Lloyd (2004) report 68 million gallons per day savings resulting from installing distribution management areas, pressure reduction, replacing and repairing water mains, leak detection and repair.
Rajala (2001) reports on program in Kansas that includes leak detection, meter testing and replacement, and bookkeeping reviews. 50 water audits were conducted and 207 million gallons on annual basis were saved as a result. The cost of the program was $339,136.
No study considering the persistence of savings from leak detection has been found.
The assumptions regarding how much earlier leaks are detected with a program than without a program are not well supported.
Confidence in Estimates
Low. To obtain reliable estimates of water conservation from leak repair, one needs to measure leakage rates and how they may change over time.
Supplier program costs may include:
- Leak detection equipment and labor.
AWWA (1999) conclude that the cost of water audits vary widely depending on factors such as the completeness of the audit, the size of the service area, and quality of utility records. In addition to meter testing, the major component of cost is labor by utility staff or consultants.
For 12” to 15” meters, reviews reported audit cost from $500-$2,500. A 1994 calibration of a 30” meter cost $600. California water system costs tend to run higher than the national averages reported by AWWA, according to the reviewers.
Reviewers also noted that leak prevention activities cost about $150 per test. Materials cost in the range of $500 to $2,000—for example—for installation of back flow devices.
As stated before Moyer et al. (1983) results of six years of leak detection, with 498 leaks detected and repaired, cost $239,062.
Limitations Leak detection equipment is evolving rapidly and cost data needs to be updated periodically.
Confidence in Estimates
Water Savings Calculation Formula(s)
Estimating the water lost from a leak can be performed with one of three methods: 1) bucket and stopwatch, 2) hose and meter, or 3) calculation using Greeley’s formula (AWWA 1999):
- Q = ( 43,767/1440 ) * A * sqrt(P)
- Q is flow in gallons per minute
- A is the cross-sectional area of the leak in square inches (or 3.14*r2 if circular hole)
- P is pressure in pounds per square inch
Factors to Consider in Applying the Formula
The formula provides only a rough approximation, not a source of measured data.
Table 1 contains results of savings calculations using Greeley’s formula for circular holes.
Table 2 contains results for leaks in joints and cracks.
Table 1 -Leak Losses for Circular Holes Under Different Pressures (gpm)
|Diameter of Hole|
|(in.)||Area of Hole (in.2)||20 psi||100 psi||200 psi|
Table 2 -Leak Losses for Joints and Cracks Under Different Pressures (gpm)
|Length of Crack|
|(in.)||Width of Crack (in.)||20 psi||100 psi||200 psi|
Source: Abstracted from AWWA 1999. Orifice coefficient is .60.
Questions to Ask
- Do you know who to ask to obtain your “unaccounted for” percentage? (Hint -operations and billing departments are sources for produced and sold water, which can be used to calculate a cursory estimate of unaccounted for water. However, a thorough audit process is needed for a fully substantiated estimate of unaccounted for water.)
AWWA (1999), American Water Works Association, “Water Audits and Leak Detection: Manual of Water Supply Practices M 36.”
Bardsley, A. and R. Lloyd, “Leakage Reduction: A Proven Alternative Resource. A Yorkshire Water Services UK Three Year Study,” AWWA Water Resources Conference Proceedings, 2004.
California Department of Water Resources (1986), “Water Audit and Leak Detection Guidebook,” with the American Water Works Association California – Nevada Section.
California Department of Water Resources, “Leak Detection Technology,” Water Conservation News, Spring 2002, URL: http://www.owue.water.ca.gov.
Farley, M., and S. Trow, “Losses in Water Distribution Networks – A Practitioner’s Guide to Assessment, Monitoring, and Control,” IWA, April 2003.
Flowers, J., “U.S. Environmental Protection Agency’s Interest in the Water System Leakage Issue,” AWWA Conference Proceedings, 2001.
Greeley, D.S. (1981), “Leak Detection Productivity,” Reference Number 1981, Water/Emergency & Management, Des Plaines, p. 111 (as noted in AWWA 1990).
Lalonde, A. “Use of Flow Modulated Pressure Management in York Region, Ontario to Reduce Distribution System Leakage,” AWWA Water Resources Conference Proceedings, 2004.
Lambert, A., “Issues and Needs in Water Loss Reduction,” AWWA Conference Proceedings, 2001.
Maddaus, L., J. Van Arsdel, and C. Woody, “Tracking Down Those Water Losses! A Case Study in Asheville North Carolina,” AWWA Water Resources Conference Proceedings, 2004.
Moyer, E. et al., “The Economics of Leak Detection and Repair,” originally published in Journal AWWA (vol. 75, no. 1, January 1983) as reported in Thorton (2002, p 241).
Moyer, E.E. (1985), “The Economics of Leak Detection: A Case Study Approach,” American Water Works Association.
T.K. Rajala, “Kansas Water Plan Programs to Reduce Unaccounted For Water,” AWWA Conference Proceedings, 2001.
Thorton, J., “Efficient Water Pressure Management as an Effective Tool for Utilities,” AWWA Water Resources Conference Proceedings, 2004.
Thorton, J., “Water Loss Control Manual,” McGraw-Hill, 2002.
Trow, S., and M. Farley, “Developing a Strategy for Leakage Management in Water Distribution Systems,” Proceedings of the IWA Conference on Efficiency Use and Management of Urban Water Supply, April 2003.
Young, A. “Advanced Water Pressure Management in the Berea-Alexander Park Supply District, Johannesburg, South Africa,” published in Thorton (2002, p 279).