Best Practices

The process of proactively seeking and fixing leaks is part of a comprehensive water loss control program. As defined by the U.S. Environmental Protection Agency (USEPA) in its report, Control and Mitigation of Drinking Water Losses in Distribution Systems [EPA 816-R-10-019, Nov. 2010]:

A water loss control program is an iterative process that must be flexible and customizable to the specific needs of a Public Water System (PWS). There are three major components of an effective water loss control program that must be repeated on a periodic basis to continually evaluate and improve the performance of a PWS. These three components are 1) the Water Audit, 2) Intervention, and 3) Evaluation.

The Water Audit

The American Water Works Association (AWWA) represented the U.S. in a five-country task force formed by the International Water Association (IWA) for the purpose of developing a best practice water audit structure for drinking water utilities. In 2003, AWWA recommended adopting use of the IWA/AWWA Water Audit Method. Since that time, the U.S. Environmental Protection Agency (USEPA), the Alliance for Water Efficiency (AWE), the Water Research Foundation (WRF), the California Urban Water Conservation Council (CUWCC) and numerous other industry associations and non-profit organizations endorse the Water Audit Method and the AWWA’s practice manuals and tools as the industry’s prevailing best practice.

The purpose of the water audit is to establish a benchmark of the types and magnitudes of different types of water losses. Water utilities have long known that total water in did not equal total water delivered and sold to customers. The imbalance between these two numbers was referred to as Unaccounted for Water. The problem was that the difference between these two numbers was comprised of multiple types of water issues. Without a solid understanding of the sources of these differences, there was little basis for pursuing remedies.

WSO slide1 Diagram courtesy of Water Systems Optimization

The prevailing best practice now entails breaking down the volume of Unaccounted for Water into multiple components. One of those components is the amount of estimated Real Losses that occur as a result of water infrastructure leaks. [The term Unaccounted for Water is now discouraged, in favor of more informative data.]

Since 2003, the AWWA recommends developing a water balance as the best practice for conducting a water audit. The water balance allows for breaking down the volume of water losses (system input volume – authorized consumption) into Real Losses (system leakage) and Apparent Losses (customer meter under-registration and unauthorized consumption).


Once the key elements of a water utility’s system losses are understood, appropriate intervention strategies can be developed. The types of intervention depend upon the types and magnitudes of  losses identified and evaluated in context of costs vs. benefits.


The AWWA methodology and tool provide multiple performance indicators to help water utilities evaluate their water loss control performance over time. Like any methodology, the  value of the outputs depend on the validity of the inputs. Accurate metering and other data are essential to understanding a water utility’s situation and the relative merits of various remediation strategies.

Types of Water Leaks

Source: Jairo Tardelhi Filho SABESP Source: Jairo Tardelhi Filho SABESP

This webpage was funded by California utility customers under the auspices of the California Public Utilities Commission

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