Best Management Practice: Distribution System Audits, Leak Detection, and Repair
A distribution system audit, leak detection, and repair programs help Federal facilities reduce water losses and make better use of limited water resources.
This page outlines best management practices for distribution system audits, leak detection, and repair across:
- Distribution System Audit
- Operations and Maintenance
- Retrofit and Replacement Options
- Case Study
Federal facilities with large campus settings and expansive distribution systems can lose a significant amount of total water production and purchases to system leaks. Leaks in distribution systems are caused by a number of factors, including pipe corrosion, high system pressure, construction disturbances, frost damage, damaged joints, and ground shifting and settling. Regular distribution system leak detection surveys can generate substantial benefits including:
Reduced water losses: Reducing water losses stretch existing supplies to meet increasing demand. This could defer the construction of new water facilities such as wells, reservoirs, or treatment plants.
Reduced operating costs: Repairing leaks saves money by reducing power costs to deliver water and chemical costs to treat water.
Increased knowledge of the distribution system: Becoming more familiar with the system, including knowing the location of mains and valves empowers personnel to respond faster to emergencies such as main breaks.
Reduced property damage: Repairing system leaks prevents damage to property and safeguards public health and safety.
Improved justification for water management: Conducting routine water audits and verifying production and end point meters results in better accounting and helps validate the need to reduce water losses.
A distribution system audit helps to quantify system losses and target leak detection and repair. A leak detection survey then identifies leak locations, pinpointing the exact location so the leak can be repaired.
Distribution System Audit
Federal installations should first complete a prescreening system audit. A prescreening audit is a preliminary estimate of losses in the system by quantifying verifiable uses in the system compared to the total supply coming into the installation. The prescreening audit helps determine the need for a full-scale system audit. The following two methods can be used (recommended every two years):
- Determine total water supply into the system over a given timeframe.
- Quantify all sub-metered uses over this same timeframe. Sub-metered uses may include buildings, reimbursable accounts, and family housing.
- Estimate unmetered uses over this timeframe. Unmetered uses may include irrigation, construction, fire suppression, and street cleaning.
- Add all verifiable uses (in step 2 and 3) and divide this number by total supply into the system.
- 5. If this quantity is less than 0.9, a full-scale distribution system audit is needed.
- Monitor minimum system flow. Perform this during unoccupied periods where flow is at the lowest level, which is typically around 3:00 a.m. or 4:00 a.m.
- If there are significant increases to the minimum system flow, it can be assumed leak related and indicates that a full-scale distribution system audit is necessary.
When indicated, facilities should complete full-scale distribution system water audits. Consider using a free water auditing software program through the American Water Works Association.
A full-scale audit is an in-depth analysis of the distribution system that includes the steps in the prescreening audit with additional steps such as mapping the distribution system, verifying accuracy of meters, and testing distribution controls and operating procedures. A full-scale audit will provide detailed data on system uses that can help quantify losses in the system. The results of the full-scale audit can help direct and prioritize the leak detection efforts.
Operations and Maintenance
The following operations and maintenance (O&M) options help Federal installations minimize leaks in a distribution system:
Manage pressure in the system to ensure that optimal levels are maintained. High pressure causes wear and tear on the system causing new leaks and increasing loss rates.
Install meters in different areas or zones of the system to monitor flow rates. Manage metered data by setting flow rate thresholds. When exceeded, indicate possible system leaks.
Institute cathodic protection for material in the system composed of metal such as pipes and tanks. Cathodic protection controls corrosion of metal surfaces by supplying an electrical current that stops the corrosive reactions.
Retrofit and Replacement Options
The following retrofit and replacement options focus on leak repair and pipe replacement:
Use leak detection devices, such as acoustic or sound-based technology that identifies leaks for repair. Water escaping from pipes creates a distinct sound that moves through the piping material. Different pipe materials transmit different frequency sound at differing lengths. There is a variety of acoustic technologies for different pipe types.
Consider installing permanent detection systems on large distribution systems that monitor for leaks 24/7 to focus leak repair efforts. Permanent systems should be used in conjunction with other leak detection techniques that pinpoint leak locations.
Pinpoint leaks by using a correlator and ground microphone that can determine the exact location of the leak.
Repair leaks or replace pipes when leaks are identified.
For specifics, consult with experts in the field. The first resource should be local or headquarters engineers, but do not overlook input from experienced contractors or other agencies.
American Water Works Association: The American Water Works Association offers resources in water auditing and loss control including manuals and resources how to find qualified service contractors.
Water Efficiency Journal Leak and Audit Articles: A series of articles related to leak detection and system audits provide information on emerging technologies and techniques.
Alliance for Water Efficiency Water Loss Control Website: An overview of water loss control and series of case studies to offer examples of water loss control programs.
Kirtland Air Force Base (AFB) performed an award-winning leak detection and repair program in 2006. The results save Kirtland AFB 179 million gallons of water each year, which is more than 16% of the total water use at the base.