Proceedings of the International Symposium on Efficient Water Use in Urban Areas


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MONITORING AND MANAGING UNACCOUNTED FOR WATER

Richard G. Sykes, Andrew K. Enos and Ronald L. Bianchetti
East Bay Municipal Utility District, Oakland, California USA

INTRODUCTION

The East Bay Municipal Utility District (EBMUD) supplies water to approximately 1.3 million people in 35 cities and communities on the eastern side of San Francisco Bay in California. Over 90 percent of EBMUD’s water supply comes from the Sierra Nevada Mountains via three 140-km (90-mile) long aqueducts. The remaining water supply is from watersheds and reservoirs in the local East Bay Hills.

Average water demand is approximately 760 million liters per day (ML/d) (200 million gallons per day or MGD). This water is produced by six water treatment plants. Two plants are operated year round, three plants are operated seasonally from 8 to 10 months per year, and the remaining plant is a standby facility. EBMUD’s water distribution system includes approximately 6,400 km (4000 miles) of pipeline, 126 pumping plants and 165 treated water reservoirs.

EBMUD has conducted a program to monitor and manage unaccounted for water. This program is an integral part of the water system operation and maintenance and is critical to ensure efficient management of our limited water supply. Benefits of managing and minimizing unaccounted-for water include:

Reduces demand on scarce water supplies and minimizes the need to develop additional supply
Reduces water and revenue losses
Reduces pumping and treatment costs
Increased knowledge of the distribution system
Reduction of property damage through improved maintenance

DEFINITION OF UNACCOUNTED FOR WATER

There is no universally applied or accepted definition of unaccounted-for water ^(1,2).
In general, unaccounted-for water is the difference between the water supplied to a distribution system and the water that leaves the system through its intended use. Some have defined unaccounted-for water as water supplied to a system less all metered water leaving the system. Other utilities use a broader definition whereby unaccounted for is all water that cannot be accounted for through measurement or estimation ⁽³⁾. The value or percentage of unaccounted-for water is an excellent overall indicator of the operating efficiency of a water system.

EBMUD defines unaccounted-for water as total water plant production provided to the distribution system minus the sum of all metered flow from the system and all unmetered authorized uses. In this definition, unaccounted-for water includes water loss from all underground distribution system piping facilities, illegal connections or theft, and inaccurate metering.

Unaccounted-for water is very difficult to calculate if a water system is not metered. If the system is partially metered, then estimates can be made to account for water leaving the system that is legitimately being used in useful ways (e.g. fire fighting, hydrant and water main flushing, water quality, etc.). It is important that water utilities recognize and estimate these uses so that they can accurately determine the magnitude of losses such as leakage, illegal connections or theft, and inaccurate metering. EBMUD’s system is metered for nearly all uses with the exception of fire hydrants. Most systems in the United States meter all residential, commercial and industrial uses.

Unaccounted-for Water Goal

A number of organizations have specified goals for utilities to use in managing unaccounted-for water. The California Urban Water Conservation Council, of which EBMUD is a member, identifies a 10 percent benchmark for unaccounted-for water ⁽⁴⁾.
If metered water sales plus other verifiable uses are less than 90 percent of water supplied to a distribution system, then steps should be taken by the utility to identify and reduce losses. In 1996, the AWWA Leak Detection and Accountability Committee recommended 10 percent as a benchmark for unaccounted-for water ⁽⁵⁾. EBMUD water loss reduction programs aim to keep unaccounted-for water at 10 percent or less.

PROGRAMS FOR CONTROLLING WATER LOSS

EBMUD controls water loss using a variety of efforts. The first is to identify the magnitude and source of that loss. The second is to review accuracy of meters used to measure system inflow and outflow. The third is to develop an appropriate leak detection program. The fourth is to have a reasonable program to respond to identified leaks. The final step is to have a pipe replacement program that helps ensure a tight distribution system. Each of these efforts is described below in general terms that might be applicable to all water systems. Examples of EBMUD experiences are provided for each.

The First Step is Identifying Water Loss

Accounting for all water use is the first step in developing a program for water loss. Determing water loss quantity requires reliable estimates of water production and use. A checklist and method for determining unaccounted-for water is provided in “Water Conservation Plan Guidelines” published by the Unites States Environmental Protection Agency (USEPA) in August 1998. (This information is available on the World Wide Web at http://www.epa.gov/OWM/genwave.htm#guideline.)

The American Water Works Association Research Foundation (AWWARF) includes a water audit procedure somewhat similar to what EBMUD uses. The water audit is an accounting of all water into and out of a distribution system to determine the efficiency of the system and to identify the location and magnitude of water losses ⁽¹⁾. There are four basic steps for a water audit:

Identify and quantify each source of water
Identify, quantify and verify authorized metered water uses
Identify and estimate unmetered water uses
Identify and estimate water loss

The water audit information is the cornerstone of determining priorities for a program to control leakage and water loss.

EBMUD’s process for estimating water loss involves measurement of all input into the distribution system and subtraction of the following items:

All metered water use from revenue and non-revenue meters (non-revenue meters include fire services, some public facilities, and EBMUD facilities)
All metered water use from portable hydrant meters supplied to contractors, cities and others for construction and municipal uses
Estimates of water system flushing and cleaning
Estimates of water loss from main breaks
Estimates of water use from fire fighting and fire hydrant testing
Estimates of leakage from distribution reservoirs

The remaining unaccounted-for water includes leakage from pipelines and underground appurtenances, meter inaccuracy, illegal connections and theft. From 1993 through 1997, EBMUD’s annual rate for this water loss ranged from 8 to 10 percent. In 1998, the figure was 12 percent. For EBMUD, a 12 percent water loss rate equates to about 91 ML/d (24 MGD). Because of this recent increase, EBMUD initiated a review of its water accounting procedure. This review is underway and results are not yet available.

Meter Accuracy and Testing

Metered water sales are the base of revenue for EBMUD and most other water suppliers. Meter accuracy is therefore of great importance to ensure accurate billing. It is also important to water conservation efforts and necessary for accurately determining unaccounted-for water. AWWARF has indicated that meter accuracy declines over time, with under-registration being typical. The AWWARF also notes that the failure rate for small meters may be as high as 3 percent. Any water utility that wishes to measure and reduce unaccounted for water must ensure reasonable meter accuracy ⁽¹⁾.

EBMUD’s water system contains approximately 375,000 metered connections. Ninety percent of these are for residential customers. EBMUD maintains two programs to ensure meter accuracy. One program focuses on small meters. Small meters are defined as those with a diameter less than 76 mm (3 inches). These small meters represent about 80 percent of the revenue billed annually. Accuracy of these devices is determined by performing periodic calibration checks on a small subset of “worst case” units. For example, EBMUD just recently completed a check on 200 of its oldest small residential meters (16mm or 5/8 inch). This check indicated that 95 percent the units were reading within the specified accuracy of the device (typically registering 98 percent to 102 percent of actual flow). Based on these periodic checks, EBMUD assumes reasonable accuracy (within manufacturers limits) of its small meters. Currently, the replacement program for small meters is as-needed based on problems identified by meter readers or customers.

A more rigorous testing program is conducted for large meters which EBMUD defines as those with a diameter of 76 mm (3 inches) or greater. EBMUD has about 2,500 meters in this size range and they represent about 20 percent of revenue billed annually. Each of these devices is checked for accuracy at least once every 2 years. If accuracy is not within specified standards for the meter type and size, then the unit is repaired or replaced as appropriate.

All water meters are read monthly or bi-monthly by trained staff. Besides reading meters, these employees detect significant changes in metered water use and identify physical or accuracy problems. The meter readers issue repair orders for about 11 percent (about 41,000 units) of all meters annually. Thus, meter readers are an important part of ensuring meter accuracy, not to mention their role in identifying leaks in the vicinity of the meter.

Another step in ensuring meter accuracy is a review by staff who prepare customer water bills. At EBMUD, these employees are trained to identify unusual changes in water use patterns. As a result, they also issue meter repair orders based on possible accuracy problems. Repair/inspection orders of this type average about 6,000 annually.

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