Detecting and repairing leaks is one of the main components of water conservation. Old or poorly constructed pipelines, inadequate corrosion protection, poorly maintained valves and mechanical damage are some of the factors contributing to leakage. Leak detection has historically assumed that all, if not most, leaks rise to the surface and are visible. In fact, many leaks continue below the surface for long periods of time and remain undetected. With an aggressive leak-detection program, water systems can search for and reduce previously undetected leaks. Water lost after treatment and pressurization, but before delivery for the intended use, is water, money and energy wasted. Accurate location and repair of leaking water pipes in a supply system greatly reduces these losses. Once a leak is detected, the water utility must take corrective action to minimize water losses in the water distribution system.

Unaccounted-for water for industrial/commercial systems should not be more than 10 percent of the total water produced. It is preferred that more than 95% of the water delivered be accounted for. Any loss of more than 10 percent in a system requires priority attention and corrective action. Advances in technology and expertise should make it possible to reduce losses and unaccounted-for water to less than 10 percent.

Every industrial and commercial water system facility should implement cost-effective water-loss control measures that will minimize distribution-system water losses. Water systems with pressurized distribution systems should promote water auditing, leak detection and leak repair as means to reduce operating costs and conserve water. The water audit can be used on systems with customer meters, while leak detection and repair can be used on any pressurized water system. The difference between produced water and the total of metered use and authorized non-metered use estimates is an indicator of the severity of unauthorized use problems or system water leaks.

Benefits of Leak Detection and Repair

Minimizing leakage in water systems has many benefits for water customers (and their suppliers). These benefits include:

• Improved operational efficiency
• Lowered water system operational costs
• Reduced potential for contamination
• Extended life of facilities
• Reduced potential property damage and water system liability
• Reduced water outage events
• Improved public relations.

Some added benefits of leak detection and repair that are difficult to quantify include:

• increased knowledge about the distribution system, which can be used to respond more quickly to emergencies and set priorities for replacement or rehabilitation programs
• more efficient use of existing supplies and delayed capacity expansion
• increased firefighting capability

Leak detection and repair programs can lead other important water system activities, such as:

• inspecting hydrants and valves in a distribution system
• updating distribution system maps
• using remote sensor and telemetry technologies for ongoing monitoring and analysis of source, transmission and distribution facilities. Remote sensors and monitoring software can alert operators to leaks, fluctuations in pressure, problems with equipment integrity and other concerns.
• inspecting pipes, cleaning, lining and other maintenance efforts to improve the distribution system and prevent leaks and ruptures from occurring. Systems might also consider methods for minimizing water used in routine water system maintenance.

Unaccounted-for Water

Unaccounted-for water includes unmeasured water put to beneficial use as well as water losses from the system. It is the difference between water produced (metered at the treatment facility) and metered use (i.e., water sales plus non-revenue-producing metered water). Unaccounted-for water can be expressed in millions of gallons per day (mgd) but is usually discussed as a percentage of water production:

Unaccounted-for water (%) = [(Production - metered use) / (Production)] x 100%.

Authorized un-metered uses include firefighting, main flushing, process water for water treatment plants, landscaping of public areas, etc. Water losses include all water that is not identified as authorized metered water use or authorized un-metered use.

Types of Leaks

There are different types of leaks, including service line leaks and valve leaks, but in most cases, the largest portion of unaccounted-for water is lost through leaks in supply lines. There are many possible causes of leaks, and often a combination of factors leads to their occurrence. The material, composition, age and joining methods of the distribution system components can influence leak occurrence. Another related factor is the quality of the initial installation of distribution system components. Water conditions are also a factor, including temperature, velocity and pressure. External conditions, such as stray electric current; contact with other structures; and stress from traffic vibrations, frost loads and freezing soil around a pipe can also contribute to leaks.

Underground Leaks

The underground piping on either side of a water meter should be maintained. Leaks in underground plumbing can be caused by many different factors, including rusting through from age or from stray electric currents from other underground utilities that can prematurely rust metallic piping, driving over piping with heavy trucks or equipment, poor initial installation, freezing and thawing of a pipeline, leaking joints or valves or transient high-pressure events such as opening and closing valves or starting and stopping pumps quickly.

Signs of underground leaks include:

• Unusually wet spots in landscaped areas and/or water pooling on the ground surface
• An area that is green, moldy, soft or mossy surrounded by drier conditions
• A notable drop in water pressure/flow volume
• A sudden problem with rusty water or dirt or air in the water supply (there are other causes for this besides a leak)
• A portion of an irrigated area is suddenly brown/dead/dying when it used to be thriving (water pressure is too low to enable distant heads to pop up properly)
• Heaving or cracking of paved areas
• Sink holes or potholes
• Uneven floor grade or leaning of a structure
• Unexplained sudden increase in water use, consistently high water use or water use that has been climbing at a fairly steady rate for several billing cycles

If any of these conditions exist at a property, there may be a leak. If a leak is suspected, a professional leak detection company may be required to pinpoint its exact location and a contractor hired to perform repairs. There are leak detection service companies listed in the yellow pages. Any utility contractor should be able to repair a leak once the location is known.

Leak Detection and Repair Strategies

There are various methods for detecting water distribution system leaks. These methods usually involve using sonic leak-detection equipment, which identifies the sound of water escaping a pipe. These devices can include pinpoint listening devices that make contact with valves and hydrants and geophones that listen directly on the ground. In addition, correlator devices can listen at two points simultaneously to pinpoint the exact location of a leak.

Large leaks do not necessarily constitute the greatest volume of lost water, particularly if water reaches the surface where they are usually found quickly, isolated, and repaired. However, undetected leaks, even small ones, can lead to large quantities of lost water since these leaks might exist for a long time.

Ironically, many small leaks are easier to detect because they are noisier and easier to hear using hydrophones. The most difficult leaks to detect and repair are usually those under stream crossings. Leak detection efforts should focus on that portion of the distribution system.

Active leak detection is crucial in identifying unreported water leakage and losses in the distribution system. Finding and repairing water losses through an active leak detection program will reduce water loss and, in many cases, save substantial money. Without a leak detection program, leaks may only be found when they become visible at the surface or when major infrastructure collapses. Active leak control will reduce expensive emergency overtime repairs and the associated liability costs. The impact on customers is also greater in emergency repair situations as is the possible impact on other infrastructure (roads, sewers, utilities) and on the environment due to possible discharges of chlorinated water. Detecting leaks is only the first step in eliminating leakage. Leak repair is the more costly step in the process. On average, the savings in water no longer lost to leakage outweigh the cost of leak detection and repair.

In most systems, assuming detection is followed by repair, it is usually cost-effective to completely survey the system every one to three years. Selecting a strategy depends upon the frequency of leaks in a given pipe and the relative costs to replace and repair them. For example, instead of repairing older, leaking mains, some argue it is preferable to replace leak-prone older pipes. Deciding whether to emphasize detection and repair over replacement depends upon site-specific leakage rates and costs.

In general, leak detection and repair result in an immediate reduction in lost water, whereas replacement will have a longer-lasting impact to the extent that it eliminates the root cause of leaks. The most important factor in a leak detection and repair program is the need for accurate, detailed records that are consistent over time and easy to analyze. Records concerning water production and sales, and leak and break costs and benefits, will become increasingly important as water costs and leak and break damage costs increase and as leak detection and rehabilitation programs become more important. Generally, the water system should keep three sets of records: (1) monthly reports on unaccounted-for water; (2) leak repair report forms and (3) updated maps of the distribution system showing the location, type and class of each leak.

Checking for Leaks

Identifying leaks can be difficult; however, at minimum the following should be performed:

• Inspect irrigation systems for obvious above-ground leaks. Extremely wet areas above an underground pipe can be an indication of a broken pipe or joint.
• Examine equipment routinely and look at exposed pipes to see if you can visually see any leaking water.
• Compare your records with the same month of previous years. While the amount of water used will vary due to weather and processes, look for sharp increases in your consumption that could indicate a leak. If you suspect a leak at your facility, take steps to get the leak fixed.

Business and Commercial Leak Detection

Costs related to leakage can add up quickly. Not only do businesses pay water and sewer charges for a leak, but there can be considerable additional costs for repairing water damage or from production downtime caused by larger leaks. Some leaks may continue for years without being noticed, finally culminating in a sudden major failure from the gradual undermining of a footing or foundation segment. In some cases, failures from a long-term leak can endanger lives.

Because leaks are continuous and can cause damage over time, checking for leaks on a regular basis can prevent considerable expense on utilities and property repairs. Common sources of leaks are toilets, faucets or showerheads, broken mechanical equipment or valves and underground piping including water service lines and irrigation systems.

Equipment Malfunction: One of the largest sources of leakage at business/commercial properties is equipment malfunction. Often these kinds of “leaks” go on for extended periods because they are not causing any damage or disruption to daily operations. Common areas where malfunctions can occur include:

• Overflow valves or float valves on cooling towers, water features, swimming pool equipment, storage tanks, etc. can malfunction in the open position allowing equipment to continuously overflow water to the sewer.
• Bypass valves can be left open following equipment maintenance, allowing a piece of equipment that is normally on a closed cooling loop to operate in a single pass mode, wasting thousands of gallons of water every day.
• Temperature control valves fail, causing substantially more water to be passed through a piece of equipment than is necessary to cool it sufficiently.
• Off/on switches or sensors can stick in the on position, running water through machinery that normally would be shut off when not in use.
• Rusting through or separation of internal parts that allow water to escape and drain from a machine that normally contains and/or recirculates the water.
• Nozzles that are supposed to shut off drip continuously or stick on.

A weekly or monthly visual inspection of water using equipment will usually uncover these types of problems.

Even businesses that do not use water as part of their operations can be harmed by water leaks. For example, it is estimated that, in an average residence, 20 or more gallons of water are lost to leakage each day, and the most common culprits are leaking toilets or dripping faucets. It is not uncommon to find toilets causing much more leakage than the average 20 gallons. Silent toilets leaks can account for up to 300 gallons of day of lost water without anybody noticing the leakage. This size of leak is very costly and should be repaired immediately. Leaks in flush-valve-style toilet are less obvious and need to be fixed by a person familiar with this procedure.

Comprehensive Leak Detection and Repair Programs

It is recommended as a best management practice for systems to attain a 10 percent or less unaccounted-for water loss in their systems. A system’s program should include auditing procedures and in-field leak detection and repair efforts. To account for system leakages, an actual annual water production volume by the supplier and an annual distribution system leakage (unaccounted-for water) expressed in percentage and volume should be prepared.

Distribution system leakage totals calculated in accordance with the formula below shall be recorded in annual percent and volume;

DSL(%) = [(TP - AC) / (TP)] x 100

Where:
DSL = Percent of Distribution System Leakage (%)
TP = Total Water Produced and Purchased
AC = Authorized Consumption

Note that:
(i) Total water produced and purchased and authorized consumption must be calculated. Elements of authorized consumption that cannot be metered, such as fire flow, must be estimated.
(ii) All or portions of transmission lines may be excluded when determining distribution system leakage.
(iii) Any water that cannot be accounted for shall be considered distribution system leakage.

Leak detection surveys using best available technologies should be completed on systems every three years and leaks fixed as part of the system's water-use efficiency program.

Leak detection and repair must be a continuous effort. The water system shall reduce system leakage to an economic minimum and repair leaks when reported and are cost-effective to repair. In addition to repairing all reported leaks, the water system should consider intervention measures to reduce components of unreported leakage and background leakage through the use of sonic leak-detection surveys, the installation of acoustic data loggers and the accelerated repair of reported leaks.

References:
American Water Works Association. 2003. Manual of Water Supply Practices. www.awwa.org.
International Water Association. 2000. Losses from Water Supply Systems. www.iwahq.org.