Once leaks are pinpointed and repaired, there is normally a direct reduction in expenses equal to the cost of producing the amount of water recovered. The production cost is the cost of water purchased from a neighboring system, the cost for energy and chemicals to produce the water in-house, or both. If 50 percent of the unaccounted for water is equal to 1,000 gallons a month and the production cost is $1/1,000 gal, then the value of that water is $1,000/month or $12,000/year. If the cost to implement a leakage control survey is $10,000, then the program would pay for itself in 10 months.

A few years ago, sonic leak detection was considered the most advanced way to detect and pinpoint leaks. This method involves using sounding equipment to listen for leak noise by making contact with system appurtenances (such as fire hydrants, valves, and meters), by listening over the line to hear the leaking water affecting the soil underground, or both. This method works well on metallic systems because the sounds produced by the leak transmit for long distances - up to 1,000 ft. (300 m) along the pipe wall, depending on leak type, pressure, and pipe size.

Sonic leak detection is not as effective on plastic piping because the sounds do not transmit very far - often only a few feet (meters). A new method has been developed that uses a nonintrusive ultrasonic device. This device straps on to the outside of the pipe, measures the rate of flow through the pipe, and records the flow data at specified time intervals in a computer file. Grant Mitchell, general manager of the East Lowndes Water Association in Columbus, MI, recently invested in this method of leak detection. He said, "The first leak we found, after only two days, paid for the equipment based on the annualized power and chemical costs of the water recovered from repairing the leak."

With this method, a zone in the system is isolated by valving, and the minimum night flow is measured and recorded by an ultrasonic device. Flow less consumption is the leakage rate within that zone. The minimum night flow can be measured within various zones of the system to prioritize leak detection efforts. Zones with excessive night flow can be investigated further by step-testing, which involves isolating sections within the zone and recording the reduction in flow. This process identifies and quantifies leakage within a specific area.

Once a cost-effective leak detection program has been implemented, then the frequency of the survey should be evaluated. A number of small water systems conduct on going monitoring of night flow measurements to immediately identify main breaks within a specific zone of the system and to track historical flow patterns to determine at what point it becomes economically feasible to implement step-tests and sonic leak surveys.

Reduced operating cost is not the only benefit of a leakage control program. Other benefits are (1) fewer overtime hours because leaks can be scheduled for repairs instead of responding to them on an emergency basis, (2) fewer unnecessary excavations because leaks can be accurately pinpointed, (3) less infiltration to wastewater treatment facilities, (4) improved public relations because the utility is an active partner in conservation, (5) reduced liability from undermining of streets and surface icing caused by leaks, and (6) improved maps because updated information is provided about the piping system.