Data Collection and Management

The water utility should track the location (using GPS whenever possible) and relative size of each leak that is detected and repaired. An estimate of the amount of water that is lost from the distribution system due to the leak.

AWWA indicates that the leakage from a hole in a pipe can be estimated using the following equation:

Q = 43,767/1,440 x A x P^0.5

Q = Flow (gpm)

A = cross-sectional area of the hole in the pipe (inches²)

P = pressure (psi)

Leakage rate can also be estimated using a bucket and stopwatch, if the pipe which is leaking can be accessed while the leak is occurring.  This method is particularly effective for measuring the flow through small leaks, however, most leaks that are detected using field observations (see leak detection BMP) are either too large or will be isolated from the water supply by the time that the pipe is accessed.

Note that AWWA's M-36 Manual has a set of tables that provide estimated leak rates for different hole sizes at different line pressures.

Water utilities should standardize how leaks are reported and tracked.  A leak repair report that identifies the following is recommended:

• Date
• Crew/staff that reported and witnessed the leak
• Location
• Leak number
• Type of leak (i.e., meter, yoke, main line, joint, service connection, other)
• What was damaged (split, broken coupling, gasket blown, crushed bell, cracked bell, hole, etc.)
• Description of the repair (i.e., repacked joint or valve, replaced line, leak clamp, etc.)
• Time required to repair leak
• Costs for repair (i.e., materials, equipment rental, labor)
• Size of leak (i.e., size of hole, type of hole (split seem, puncture, etc.)
• Estimated leakage (gallons)
• Estimated age of leak/how determined
• Pipe material
• Cause of leak (if known)
• How leak discovered (tracking reported leaks versus unreported leaks can help the utility determine whether it is reactive to customer complaints and observations, or is proactive finding leaks before they are reported)

The water utility should track the costs of leak repair associated with each leak, and collectively for all leak repair over a single year.  The water utility should also track the costs related to implementing leak detection activities to the extent that leak detection is conducted.  Finally, the utility should track the cost of capital improvement projects that are conducted by the utility.  These costs should include pipe replacement, new pipe installations (into location that previously did not have pipe) and replacement and/or installations of new appurtenances and submeters. 

The utility should only be doing those repairs and related infrastructure replacement and upgrades that are economically justified to the utility.  Therefore, these data that are being collected related to leak detection and repair can be used directly to determine the economic viability of expanding leak detection programs, creating district metered areas, or upgrading infrastructure.

Estimating total non-revenue water in a system will require the operator to track total water losses as well as unbilled water consumption.  This is performed by tracking authorized and unauthorized consumption.  Authorized consumption includes all billed consumption both metered and unmetered.  An example of unmetered water billings is construction water stand pipe sales or hydrant use.  Unbilled water consumption can also be authorized - both metered and unmetered unbilled uses.  Metered unbilled uses may include town hall, town park, town shops, etc. Unmetered, unbilled uses may include, but not be limited to:

• Line and system flushing
• Authorized use of fire hydrants and stand pipes (where the utility may provide permission for use of construction water or similar, but metering of the water removed from the distribution system does not occur)
• Street cleaning use,
• Fire fighting.

For unmetered uses, the operator can calculate volumes of water use from pumping rates and time periods, volume of receiving vehicles (e.g., size and percent fill of a water tank with known storage tank volume), etc. Unbilled volumes should be estimated for each month.

The above lists describe those water uses that are considered to be types of authorized consumption - since the utility is aware of these uses.  Unauthorized consumption, on the other hand, are those water uses that occur without the knowledge of the utility. Unauthorized consumption constitutes one type of real water loss for the utility.  Other water losses include leaks and other real losses, as well as apparent water losses associated with customer metering inaccurancies and systematic data handling errors.  Total water loss is the combination of real and apparent losses. 

The AWWA Water Audit Tool helps utilities to estimate and track these different comnponents of non-revenue water.

For those distribution systems that have meters installed on distribution lines to help isolate leaks (using district metered areas (DMAs)), and determine flows into specific portions of the overall distribution system, readings of these meters should be collected daily at a minimum, and more often if possible, since close monitoring of these data are needed to utilize this practice.  Ideally, the DMA meters would be instrumented such that electronic readings would be provided in real time to the water system operator, such that significant leaks in the distribution system could be quickly detected and located.

Data should be collected whenever leaks are repaired and pipe is replaced.  A full record of the distribution system location, material, and pipe attributes (e.g., diameter) should be maintained.  Ideally, the map will be maintained electronically, such that it can be easily updated, and past as well as current information regarding the distribution system can be archived.  The water system operator should also consider collecting global positioning system (GPS) coordinates (or similar) of all work conducted by the utility to strive toward creating a database that can facilitate re-location of the pipe and its appurtenances. 

Note that distribution systems include all those pipe and appurtenances that are owned and maintained by the utility between the treatment facility and the customer meter (including a portion of the customer service line).  After the customer meter, the customer typically owns and maintains their portion of the service line.