Distribution System Audits, Leak Detection, and Repair

A distribution system audit, or leak detection and repair program, may help federal facilities identify and reduce water losses and be better stewards of water as a resource.

Overview

. 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 and repair programs 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 supply facilities such as wells, reservoirs, or treatment plants.
  
• Reduced operating costs: Repairing leaks saves money by reducing costs to deliver and treat both supply and sewer water.
  
• Increased knowledge of the distribution system: Becoming more familiar with the system, including size and type of piping materials, and 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 result 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 calculated 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).

1. Determine total water supply over a given timeframe (typically one year).
    
2. Quantify all submetered uses during this same timeframe. Submetered uses may include buildings, reimbursable accounts, large process water using applications, and family housing.
    
3. Estimate unmetered uses during this timeframe. Unmetered uses may include irrigation, construction, fire suppression, and street cleaning.
    
4. Add all verifiable uses (in step 2 and 3) and divide by total supply into the system.
    
5. If this quantity is less than 0.9, a full-scale distribution system audit is needed.

Or:

1. Monitor minimum system flow. Perform this during unoccupied periods where flow is at the lowest level, which is typically around 3 a.m. or 4 a.m.
    
2. If there are significant increases to the minimum system flow over time, it can be assumed to be leak related and indicates that a full-scale distribution system audit is necessary.

When needed, facilities should complete full-scale distribution system water audits. 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 about the age, size, and type of piping, as well as system uses that can help quantify losses. 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.
  

Leak Detection and Repair Considerations

Below are technical considerations for leak detection equipment and distribution system repair.

• Use leak detection devices such as acoustic or sound-based technology that identify leaks for repair. Water escaping from pipes creates a distinct sound that moves through the piping material. Different pipe materials transmit different frequencies at differing lengths, creating distinct sounds. There are a variety of acoustic technologies for different pipes.
  
• 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, which can determine the leak’s exact location.
  
• Significant leaks should be repaired immediately, and lengths of pipe with many leaks should be considered for replacement.
  
• For specifics, consult with experts in the field. The first resource should be local or headquarters engineers but input from experienced contractors or other agencies should also be considered.