Page 140 - Water Loss Control

122 Cha pte r T e n

these models nonrevenue water has generally been treated very simplistically as a fixed
residual. Accordingly, a separate series of concepts for modeling water loss has been
developed since the early 1990s for the following components of nonrevenue water:

• Apparent loss (customer meter inaccuracy, systematic data-handling error in
billing systems, and unauthorized consumption)
• Real loss (leakage and overflows)
• Pressure/leakage, pressure/consumption, and pressure/break (frequency
relationships)

The reliability and effectiveness of water loss modeling makes it a standard part of
the loss management practitioner’s tool kit.
It is important to emphasize that water loss management models are not the same
tools as hydraulic models. Many water utility personnel, consultants, and contractors
have used or seen a hydraulic model, which mathematically calculates values of water
flow and pressure in a distribution network, subject to specific inputs and consumption
patterns. Hydraulic models are an extremely powerful tool for distribution system
analysis, allowing the operator to simulate varying operating scenarios within the sys-
tem. However, the concepts used for simulating water loss management in most
hydraulic models are often oversimplified, to the point where the estimated current
leakage is nominally distributed globally around the nodes of the model; and assumed
to be fixed over time and pressure-invariant. While such simplified assumptions may
be valid for modeling flows and pressures in water distribution piping systems, they
are not valid for models which seek to quantify key water loss components.
The water loss modeling approaches discussed include
• Top-down water audit spreadsheet models
• Component analysis of apparent (nonphysical) losses
• Component analysis of real (physical) losses, such as the breaks and background
estimates (BABE) model
• The fixed and variable area discharge (FAVAD) concept for modeling
pressure/leakage rate relationships and pressure/consumption relationships
and making predictions
• Pressure/break frequency analysis concepts for making predictions of the
reduction in break frequency on mains and services with reduction in
operating pressure
• Application of component analysis and FAVAD concepts for night-flow
analysis in discrete zones or district metered areas
• Consumption analysis models
• Short run economic leakage levels

10.2 Top-down Water Audit Spreadsheet Models
The water audit methodology recommended for use in this publication was jointly
developed by the International Water Association (IWA) and the American Water Works