Page 97 - Water Loss Control

Evaluating W ater Losses 79

• A meaningful comparison of water audit results and performance indicators
can be undertaken, independent form location, size, and operational character-
istics of the water supply system.

7.4 The IWA/AWWA Recommended Standard Water Audit
The top-down water audit is basically assembled in two steps:

1. Quantification of all individual water consumption and water loss components,
via measurement or component based estimation
2. Undertaking the standardized water balance calculation

This section explains the recommended water audit approach and each component
of the water audit. The effort required to conduct a top-down water audit is relatively
modest depending on the availability and quality of data. The top-down audit also
helps to identify components that require further validation.
6
The components of the water balance as shown in Fig. 7.1 can be measured, esti-
mated, and calculated using a variety of techniques. Ideally, all components of the water
balance (excluding those components that are calculated by adding or subtracting other
components) should be based on measurements. However, in reality estimates will
need to be made especially the first time a water balance is established. Once the com-
ponents needing estimation are identified it is best practice to put actions in place that
allow to meter the component or to improve the estimation process. Validation of water
balance components is an important and integral part of conducting a water balance.
Sensitivity analysis and the use of 95% confidence limits are best practices to assess the
impact which individual water balance components have on the overall accuracy of the
calculated volume of nonrevenue water and real and apparent losses.
A water balance should be established annually and before establishing the water bal-
ance it is important to determine the audit period (e.g., fiscal year or calendar year) and the
system boundaries. The units of the water balance components must also be chosen and
standardized so that the same units are used for each component of the water balance.
The calculation procedure for the water balance is as follows:
• Obtain system input volume and correct for known errors.
• Obtain components of revenue water, calculate revenue water which equals
billed authorized consumption.
• Calculate nonrevenue water (= system input − revenue water).
• Assess unbilled authorized consumption.
• Calculate authorized consumption [= (billed + unbilled) authorized
consumption].
• Calculate water losses (= system input − authorized consumption).
• Assess components of apparent losses, calculate apparent losses.
• Calculate real losses (= water losses − apparent losses).
The following subsections explain the various steps of a water audit based on the
AwwaRF report “Evaluating Water Loss and Planning Loss Reduction Strategies. ”6