Page 112 - Water Loss Control

94 Cha pte r Se v e n

The above equation explains the standard approach for calculating an aggregated
confidence limit based on accumulation of error on derived values. Table 7.5 provides
an example of the calculation of the 95% confidence limits and variances relevant for
the calculation of 95% confidence limits for nonrevenue water.
Since the real losses have a confidence limit that is an accumulated value based on
the variance related to each component of the water balance it is very important to
accurately assign 95% confidence limits to all components of the water balance in order
to see which of the components has the biggest impact (which components have the
highest variance) on the confidence related to the calculated real loss volume. Once this
information is available, it is best practice to take actions (e.g., improving the accuracy
of metering devices or installing new metering devices where no meter was in place) in
order to improve the confidence related to the real loss volume by improving the confi-
dence related to those components that showed the highest variance.

7.9 Conclusion
The IWA/AWWA standard terminology and water balance methodology and the use of
95% confidence limits, together with the equation for unavoidable annual real losses
and the recommended performance indictors such as the infrastructure leakage index
(ILI), are the basis for a rational assessment of water loss volumes allowing meaningful
comparisons of water loss management.
Examples of free and commercial water audit software and related water balance
results are shown in Chap. 10.

References
1. Alegre, H., W. Hirner, J. Baptista, et al. “Performance Indicators for Water Supply
Services.” Manuals of Best Practice: IWA Publishing, 2000. ISBN 1 900222 272.
2. Alegre H, JM. Baptista, E. Cabrera Jr, et al. “Performance Indicators for Water
Supply Services,” 2nd ed. Manuals of Best Practice Series. IWA Publishing, 2006. ISBN
1843390515.
3. Kunkel, G. et al. “Applying Worldwide Best Management Practices in Water Loss
Control.” Water Loss Control Committee Report. Journal AWWA. 95(8):65, 2003.
4. Office of Water Services. UK. “Leakage and the Efficient Use of Water.” 1999–2000
Report. ISBN 1 874234 69 8.
5. Fanner, V. P., R. Sturm, J. Thornton, et al. Leakage Management Technologies. Denver,
Colo.: AwwaRF and AWWA, 2007.
6. Fanner, V. P., J. Thornton, R. Liemberger, et al. Evaluating Water Loss and Planning Loss
Reduction Strategies. Denver, Colo.: AwwaRF and AWWA, 2007.
7. Lambert, A., D. Huntington, and T. G. Brown. “Water Loss Management in
North America: Just How Good Is It?” AWWA Distribution Systems Symposium,
New Orleans, September 2000.
8. Lambert, A., T.G. Brown, M. Takizawa, et al. “A Review of Performance Indicators
for Real Losses from Water Supply Systems.” AQUA. Decemeber 1999.
9. Lambert A. O., S. Myers, and S. Trow. Managing Water Leakage: Economic and Technical
Issues. Financial Times Energy Publications, 1998.