Water Loss Control

Implementation of a system-wide water audit focuses upon quantifying customer consumption and volumes of real and apparent losses based on the best practice developed in 2000 by IWA/AWWA Water Audit Method[1].  The method that was developed by the AWWA allows the operator to reveal the destinations of water supplied throughout the distribution system and to quantify volumes of consumption and loss.  Imperative to the success of this method is a robust set of data that characterizes meter accuracy and all those components of water use that are described in the figure provided below.

The AWWA Water Audit methodology promotes a process of data collection and assessment that leads to the characterization of real and apparent losses; providing the water utility with a map of needs and potential programs that can improve water distribution and billing efficiencies.  The process involves evaluating:

• Production supply
• Billings
• Apparent losses
• Real losses

In accordance with AWWA recommendations, a system wide water audit should be conducted annually by consciencious water utilities to support water loss control.  The complete water audit methodology is an eleven step process detailed in this table. 

There are three levels of recommended auditing procedures, each adding increasing refinement.  Most utilities should begin with the top-down approach, as described below, before proceeding to more complex and rigorous programs.  Beginning with the top-down approach, an operator can assess the status of data availability and information required to support more refined analyses, such that future auditing can be performed after improvements are made to data collection processes and procedures (see data collection and management BMPs).

Regardless of which audit method that is used, utilities should utilize the AWWA auditing software (descibed in the Data Analysis Section of this BMP) to help standardize their data collection and reporting, and allow for the consistent tracking of wate loss information within and between utilities.

Top Down Approach – the initial desk-top process of gathering and analyzing information from existing records, procedures, data, and other information systems.  Key data collection for this level of analysis includes water production and treatment volumes (preferably on a daily to monthly basis), customer water delivery records (preferably on a monthly basis), metered, unbilled water use (preferably on a monthly basis), and estimates of unmetered water uses.  A key set of assumptions that typically will need to be made to conduct these types of audits will be the percent of customer meter and production, master meter inaccuracies.

Component Analysis – This audit method expands the data collection from the top-down approach to include developing estimates for leakage volumes based on the nature of leak occurrences and durations.  This technique can also be used to model various occurrences of apparent losses by looking at the nature and duration of estimated real loss.

Bottom-Up Approach – This technique is used to validate the top-down results with actual field measurements such as leakage losses (calculated from integrated zonal or district metered area night flows).  Field data is also collected to determine meter accuracy via physical inspections of customer properties to characterize apparent losses from inaccurate, defective, or vandalized customer meters, and to identify unauthorized consumption.  Finally, process flowcharting of customer billing systems can be used to identify systematic billing errors.

Once the water audit data has been collected, a water balance calculation is developed to characterize water losses – both real and apparent – to the extent feasible.  A preliminary assessment of water loss can be obtained by gathering available records and placing data into the water audit worksheet such as is available on the AWWA website at  http://www.awwa.org/resources-tools/water-knowledge/water-loss-control.aspx.  The summary data from the water audit is shown in the water balance, which compares the distribution system input volume with the sum of customer consumption and losses (estimated and known).

A simplified table, shown below, may also be used for small systems.

Example of a Simplified Water Balance

Category	Estimated Value	Data Validity Score	Comment
Water Supplied	(in 1000 gallons)	(grade 1 to 10)	(related to the grading)
Produced Groundwater	15,112	9	100% of water sources are metered
Master Meter Accuracy	.97	2	Daily production readings scribed on paper, no adjustment for changes in storage volumes
Total Water Supplied	15,577
Authorized Consumption
Billed Metered	8,926	6	Manual meter reading, limited meter accuracy testing
Billed Unmetered	0	2	Written policies do not exist for tracking billed unmetered accounts
Unbilled Metered	0	2	Written policies do not exist for tracking unbilled metered accounts
Unbilled Unmetered (a listing of some unmetered uses are provided in the table below)	447	4	Extent of unbilled unmetered partially known and some procedures exist to document uses (e.g., fire hydrant flushing, filter backwash)
Total Authorized Consumption	9,373
Water Losses
Total Water Loss
= Total Water Supplied – Total Authorized Consumption	6,204
Apparent Losses
Unauthorized Consumption	0	2	Unauthorized consumption is not known or tracked
Customer Meter Inaccuracies	893	4	Reliable recordkeeping exists; meter information is improving as meters are replaced.    Meter accuracy testing is conducted annually for a small number of meters.  Limited number of oldest meters replaced each year.  Inaccuracy volume is largely an estimate, but refined based upon limited testing data.
Systematic Data Handling Errors	0	4	Policy and procedures for permitting and billing exist but needs refinement.  Computerized billing system exists, but is dated or lacks needed functionality.  Periodic, limited internal audits conducted and confirm with approximate accuracy the consumption volumes lost to billing lapses.
Total Apparent Losses	893
Real Losses (Current Annual Real Losses (CARL))
CARL = Total Water Loss – Total Apparent Losses	5,311
Non-Revenue Water
= Total Water Loss + Unbilled Metered + Unbilled Unmetered	6,651

Note that the power of the water balance calculation lies in the earnest evaluation of those data used to character water quantities.  Estimated values may be used to support completion of the task, however, the operator must be aware of the limitations of any analysis completed based on estimates.  It is suggested that for best results, the operator should test variations in estimated values, to characterize potential ranges of real and apparent losses based on unknown or unattainable information.  For example, if the volume of unmetered water is not known, the operator can estimate ranges for unmetered water based on expected uses (see table below for unmetered water uses identified during previous water audits conducted for small water users in the lower Arkansas River Valley.

Note that one of the attributes of the AWWA Audit Tool relates to tracking the quality of the data being collected and used by the utility in developing the water audit and calculating water loss.  Water auditing, although a vital part of any utility water loss program, is still in its infancy as a best practice for most utilities - large and small.  Therefore, grading current data quality, and making improvements to data quality over time, is one key objective to the overall water audit approach as recommended by AWWA. 

Additional discussions of the development and use of these audit data and calculation are provided in the Water Distribution Data Collection and Management section of the BMP Tool Box .

 

Selected Unmetered Water Uses Identified in the Lower Arkansas River Basin

Church	Other Water Treatment Plant Uses
Construction Water (from hydrants and/or standpipes)	Street Cleaning
Filter Backwash	Sewer Collection Cleaning
Fire Suppression	Town Hall
Firehouse	Town Shop
Hydrant and Line Flushing	Town/City Parks

Note that one of the attributes of the AWWA Audit Tool relates to tracking the quality of the data being collected and used by the utility in developing the water audit and calculating water loss.  Water auditing, although a vital part of any utility water loss program, is still in its infancy as a best practice for most utilities - large and small.  Therefore, grading current data quality, and making improvements to data quality over time, is one key objective to the overall water audit approach as recommended by AWWA. 

Selected Unmetered Water Uses Identified in the Lower Arkansas River Basin

Church	Other Water Treatment Plant Uses
Construction Water (from hydrants and/or standpipes)	Street Cleaning
Filter Backwash	Sewer Collection Cleaning
Fire Suppression	Town Hall
Firehouse	Town Shop
Hydrant and Line Flushing	Town/City Parks

Billing is the most common interaction between the water utility and its customers; and it is the most critical part of the relationship, since for any organization, revenue generation is paramount to sustainability, for without cash flow, the utility cannot meet its financial obligations.  Therefore, billing practices and protocols are a vital component of any utility’s operations.  Billing also can be used to provide important messaging to the customer – especially messaging related to over use of water.  However, messages contained in a water bill related to the over use of water is best provided to a customer within a short time of actual water use such that a behavioral change can be implemented.  Timely billing for water use to create positive cash flow for the utility and to provide customers with feedback on their water use is an important tool for utilities to use to maintain fiscal independence and to help instill a culture of water use efficiency.