Infrastructure Development Since 1981
Infrastructure Development Since 1981
Leak Audit Procedures
Leak detection is just the first step. To minimize leakage loss, a water supply system must have a program of continuous audits, of which leak detection is just a part. A full-scale audit program should be performed at least annually with complete analysis of the leak data—not just for the current audit, but accumulated data records over time. A proper audit examines the accuracy and completeness of the system’s entire leakage database. This data does not just include reading on the leaks themselves, but also indirect measurements of potential leaks such as customer billing and receipts, along with flow meter and pressure gauge readings.
Though typically represented in a tabular format, audit data becomes most useful when portrayed geographically with data superimposed on maps of the water system that is being audited. This visual representation makes it easy to identify and isolate problem spots where leaks may be occurring. Graphically, pressure readings can be used to create pseudo-hydrostatic contours representing areas of low and high pressure. Low pressure zones thus revealed are another danger sign that a leak may be occurring in these areas. Similarly, flow measurements as represented by two-dimensional graphs (with flow rates represented by the y axis and pipe segment length shown by the x axis) can also show potential leak points.
Audits are typically costed by the mile, and they are not cheap (especially for large water supply systems). But they are essential and are far less expensive than continued water loss. Audits provide update information on system performance, tagging what is failing and (more importantly) highlighting those areas that are functioning properly. This is important with regard to evaluating previous maintenance and repair operations prompted by the results of previous audits. In short, a water system audit provides its own information feedback loop. As a side benefit to the audits, complete inventories of the water system’s equipment, valves, and fittings can be collated.
In this age of automation, many tasks still require the hands-on touch of human operators. A water leakage audit is one such task. The easiest time to perform those audits is during off-peak hours (such as the very early morning). With most people asleep at these hours, water usage should be relatively low. However, if water distribution actually increases, it is a clear indication that leaks are occurring in the pipe system. Since this initial measurement only lets the operator knows that leaks are occurring (but not much else), it represents only a preliminary step.
The next step is to identify all potential sources of water feeding into the water supply system and sum up their measured flow rates (gallons per day). This gives the baseline value for the amount of water that should be flowing through the system and through each pipeline network subsection. Next, flow meter readings should be tallied up. This provides hard field data (adjusted for potential meter error) on actual water usage flow rates. Then water flows entering the system can be compared with water usage exiting the system to determine the gross magnitude of water leakage.
After this amount is determined, the audit can break down water usage by individual customers (residents, businesses, commercial and industrial facilities, rental units, etc.). This involves both a thorough review of the data from the last year’s audit and the meter readings over the past year. Increases in flow rates indicate that the customer has either increased its usage due to expanded operations and increased economic activity, or that the customer itself has unreported leaks. If the latter is the case, it is up to the customer to find and repair any leaks that are occurring on his side of the flow meter. The water utility is only responsible for leaks on the street side of the meter.
With each pipe segment of the water distribution system defined by flow and pressure monitoring points, both the approximate location and amount of water being lost at a leak can be determined. The manual detection can then proceed to find the precise location of the water loss. The kind of leaks can vary considerably and can include illegal water taps, broken and malfunctioning meters, leaking pipe fittings and fixtures, and worn out valves. In addition to pipeline leaks, leaks can occur in water storage structures such as water towers, storage tanks, and reservoirs.
Lastly, a thorough review of the data and associated paperwork needs to be performed. In many cases, water losses are not physical losses. Instead, they are the result of poor bookkeeping and sloppy data entry. Since this is a problem caused by human error, human review and re-entry of the data is necessary for correction.