Page 141 - Water Loss Control

Modelling W ater Losses 123

Association (AWWA) and published in 2000. By compiling a water audit using the stan-
dardized IWA/AWWA methodology, water utility auditors gain an understanding of
the nature and extent of their system water loss volumes and, via the validation pro-
cess, allows the utility to calculate the mathematical confidence in those annual vol-
umes. Good management of any resource requires that the supplier maintains accurate
records of transactions and deliveries of the commodity provided to its customers.
A water audit has exactly that goal, tracking and accounting for every component of water
in the cycle of delivery. The water audit typically tracks and validates the volumes of water
from the site of withdrawal or treatment, through the water distribution system up to the
first point of customer consumption. The water audit usually exists in the form of a work-
sheet or spreadsheet that details the variety of consumption and losses that exist in a water
system. The water balance itself is a summary of all the components of consumption and
losses in a standardized format. Every unit of water supplied into the system needs to be
assessed and assigned to the appropriate component. Once volumes of valid authorized
consumption and losses (apparent and real) have been assigned, the cost impact of these
components can be calculated. Subsequently, the water utility will be able to select the
appropriate tools for intervention against real and apparent losses as discussed further
in Chaps. 11 to 19 of this manual.
Several effective top-down water audit spread-
sheet models are available for free download. In
2006, the AWWA Water Loss Control Committee
It is easy to program a
launched its free water audit software, which can be
downloaded from www.awwa.org. Instructions for spreadsheet to automatically
use of this top-down model are provided with the perform audit calculations.
software; however, instructions to conduct a However, the operator must
detailed, bottom-up water audit using the same fully understand the concepts
methodology are provided in the third edition of the being modeled—very useful
AWWA M36 publication Water Audits and Loss Con- and user-friendly spreadsheets
trol Programs (proposed 2008). This publication is are available for free from sev-
also compiled by the AWWA Water Loss Control eral sources, including AWWA
Committee. Table 10.1 provides an example using
the World Bank, and various
the AWWA free software, showing the input and consultants, see References.
output from the top-down water audit for the Phila-
delphia Water Department (PWD) for its fiscal year
ending June 30, 2006.
The AWWA’s free water audit software is an excellent tool that water utilities can
utilize to start the auditing process in a top-down manner. However, as the utility pro-
gresses with more detailed, bottom-up auditing, it becomes advantageous to incorpo-
rate 95% confidence limits as discussed in Chap. 7. Table 10.2 illustrates an example of
a water balance compiled using free water audit software that is available from the
World Bank. The example shows the resultant statistical confidence value in each key
component of the water balance.
A number of other software packages are available which offer additional features
including variance analysis (Aqua Solve, LEAKS/PIFastCalcs, and the like). The Aqua
Solve package is shown in Tables 10.3 and 10.4. Table 10.3 shows a balance from San
Francisco Public Utilities Commission (SFPUC) and Table 10.4 shows how variance
analysis can be used to identify the components which have the most impact on the
aggregated uncertainty of the water loss components.