Water Audit Process Introduction

A reliable water audit methodology was developed jointly by the American Water Works Association (AWWA) and International Water Association (IWA) in 2000.  The water balance of this methodology is given below and shows schematically the various components in which water volumes are tracked. 









(corrected for known errors)












Billed Authorized Consumption



Billed Metered Consumption

(including water  exported)





Billed Unmetered Consumption

Unbilled Authorized Consumption

Unbilled Metered Consumption





Non-Revenue Water




Unbilled Unmetered Consumption





Water Losses


Apparent Losses

Unauthorized  Consumption

Customer Metering Inaccuracies

Data Handling Errors



Real Losses

Leakage on Transmission and Distribution Mains

Leakage and Overflows at Utility’s Storage Tanks

Leakage on Service Connections up to point of Customer metering

All data in volume for the period of reference, typically one year

Water Balance of AWWA/IWA Water Audit Methodology

The water balance tracks – from left to right – how a water utility supplies water volumes from source to customer, and provides the format for the utility to quantify amounts of billed and lost water. 

The most convenient way for a water supplier to compile a water audit is by using the AWWA Free Water Audit Software© available from AWWA.   The software may be downloaded here

The software exists in MS EXCEL® spreadsheet software and is designed as a basic package that is useful for water utility personnel who aren’t familiar with the AWWA/IWA methodology.  If you work for a water utility, or are merely interested in the water audit process, you are urged to download the AWWA Free Water Audit Software© and begin entering actual or estimated data.

Fundamental to the AWWA/IWA Water Audit Methodology is the distinction that treated drinking water ultimately goes to two places: authorized consumption by consumers (its intended use), and a portion to losses (through inefficiencies).  Within the component of losses, two broad types exist:

  • Apparent Losses – are the “paper” losses that occur in utility operations due to customer meter inaccuracies, billing system data errors and unauthorized consumption.  In other words, this is water that is consumed but is not properly measured, accounted or paid for.  These losses cost utilities revenue and distort data on customer consumption patterns.
  • Real Losses – are the physical losses of water from the distribution system, including leakage and storage overflows.  These losses inflate the water utility’s production costs and stress water resources since they represent water that is extracted and treated, yet never reaches beneficial use.

No More “Unaccounted-For” Water

Research has found that dated practices of calculating “unaccounted-for” water varied so widely in utilities around the world that the term had no consistent meaning.  A fundamental concept of the AWWA/IWA Water Audit Methodology is that all drinking water can be accounted-for, via metering or estimation, as either a form of beneficial consumption or wasteful loss.  Hence no water is “unaccounted-for”.  It is recommended by AWWA to avoid use of the term “unaccounted-for” water, referring instead to the specific term “Non-revenue water”, shown in the above figure.  Additionally, the “unaccounted-for” water percentage – a simplistic measure of water not billed – as been found to be a very imprecise performance indicator and should also be avoided.  The AWWA/IWA Water Audit Methodology features an array of robust performance indicators that are calculated in the AWWA Free Water Audit Software©.

How Prevalent is the use of Water Audits in the Water Utility Sector?

Historically, the water auditing process has been in use inconsistently and sporadically in North America and this represents perhaps one of the greatest shortcomings in an otherwise highly reliable utility services sector.  Many responsible utility managers compile at least a cursory water audit each year; however, without specific requirements, most of the thousands of North American water utilities conduct infrequent water audits at best, and therefore are likely suffering notable losses without being adequately cognizant of the actual volumes of lost water.

More Information

AWE Water Loss Control Introduction 

Case Studies - The Emerging Use of Water Audits Among US Water Agencies 

Water Loss Control - What Can Be Done?