In addition to the direct loss of water, there are costly energy losses associated with municipal water loss as a result of pipeline leaks. As a single service category, municipal water utilities are the largest user of electricity in the US (Source: Von Sacken, 2001). All that electrical power is for naught if the pumped water ends up spilling out of the system. The damage done to adjacent infrastructure is another significant, if indirect, cost. Old, damaged infrastructure (shifting and dislocating pipelines, roadwaypotholes, shifting and sinking structural foundations, etc.) is afinancial time bomb.
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, auditdata becomes most useful when portrayed geographicallywith 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 anotherdanger 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 notcheap (especially for large water supply systems). But theyare essential and are far less expensive than continued waterloss. Audits provide update information on system performance, tagging what is failing and (more importantly) highlighting those areas that are functioning properly. Thisis important with regard to evaluating previous maintenanceand repair operations prompted by the results ofpreviousaudits. In short, a water system audit provides its own information feedback loop. As a side benefit to the audits, completeinventories of the water system’s equipment, valves, and fittings can be collated.
In this age of automation, many tasks still require thehands-on touch of human operators. A water leakage auditis 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 flat. However, if water distribution actually increases, itis a clear indication that leaks are occurring in the pipe system. Since this initial measurement only lets the operator know thatleaks 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 hardfield data (adjusted for potential meter error) on actual waterusage 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 breakdown water usage by individual customers (residents, businesses, commercial and industrial facilities, rental units, etc.).This involves both a thorough review of the data from thelast year’s audit and the meter readings over the past year. Increases in flow rates indicate that the customer has eitherincreased its usage due to expanded operations and increasedeconomic 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 systemdefined by flow and pressure monitoring points, both theapproximate location and amount of water being lost at a leak can be determined. The manual detection can then proceedto find the precise location of the water loss. The kind ofleaks 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 associatedpaperwork needs to be performed. In many cases, water lossesare not physical losses. Instead, they are the result of poor bookkeeping and sloppy data entry. Since this is a problemcaused by human error, human review and reentry of the data is necessary for correction.
EMERGING LEAK DETECTION TECHNOLOGIES—INSIDE AND OUTSIDE
Detecting leaks within a customer’s facility is not so much a matter of visibility, but of vigilance and continuous monitoring. New technologies are emerging that allow customers topinpoint leaks within their facilities with a higher degree ofaccuracy than the traditional methods of water leak detection such as spot detectors, which detect leaks at a single point (such as a curbed area under a piece of equipment). Though economical and easy to use, spot detectors can only detectaccumulated water in contained or low points. Water thatdoesn’t touch the spot detector’s probes will not be detected.An improvement on this system utilizes non-conductive sensing wire (which avoids shorting out if it comes into contact with metal surface or projections) and can detect any fluid, not just water.
Intelligent cable sensors are just one area of technological development. Each new advance will have to be rigorously evaluated for general usefulness and specific applicability. The factors used to evaluate new technology include: breadth of application and how many uses it can be applied to; ability to adjust sensitivity to different liquid amounts; the ability toquickly reset its readings and reestablish its sensing operations; ease of installation; scalability and adjustment to future expansions; and ease of integration into the existing control andmonitoring system. Future technological advances must pass all of these hurdles to find acceptance among both customers and utilities.
MAJOR SUPPLIERS
Hermann Sewerin GmbH manufactures electro-acousticwater leak detection devices, noise loggers, correlators, tracer gas, and flow analysis equipment. Their Aquaphone A50 is a reasonably priced entry-level model for professional acoustic water leak detection. Its A50 receiver, UM 50 microphones,and TS 50 test rod allow for easy pre-location and pinpointing of leaks. Compact and easy to carry, when equippedwith digital radio it avoids cables that can restrict movement.In addition to spot checking for leaks,their SePem noise data logger allowsfor continuous monitoring. The SePem 155 is designed for permanent use; they are magnetically attached to valve rod extensions, hydrants, or other metal fittings. The SePem 155 is designed for mobile use and temporary installation at key points along specified sections of pipe networks. More specific measurements are carried out by the AquaTest T10 test rod. This is used on objects that lie deep under the ground surface with easily screwed-on extensions for greater reach. It displays current noise levels, previous noise levels, and current noise intensity visually on a digital screen in the form of bar graphs.
