Reliable operational Performance Indicators are critical to address water losses

High levels of water losses in distribution systems (both real and apparent losses) continue to burden water companies and customers around the world: water losses vary from very low to unsustainably high. Pressure management, and finding and fixing leaks to reduce real (physical) losses are part of a straightforward way of addressing water quality issues, as well as addressing water conservation. Despite much progress being towards addressing water losses in distribution systems, losses continue to exceed economic levels.

At the recent IWA Specialist Conference on Benchmarking and Performance Assessment in Vienna, Austria, it was stated that, “Everyone knows the percentage of System Input Volume must not be used for target-setting and/or making technical comparisons”. Nevertheless, the percentage of System Input Volume (SIV) and percentage of Water Supplied (equal to SIV minus the water exported) continue to be used for these purposes, predominantly because they are traditional and easy to calculate.

The 3rd Edition of the IWA Manual of Best Practice Performance Indicators for Water Supply Systems, published this year, lists three reliable indicators that are available for real losses:

  • Real Losses per connection (lt/conn/day when system is pressurised), for urban distribution systems;
  • Real Losses per mains length (lt/km/day when system is pressurised), for bulk supply and low service connection density (rural) distribution systems; and
  • Infrastructure Leakage Index (ILI): the ratio between actual real losses and an estimate of the minimum real losses – calculated using the Unavoidable Annual Real Losses (UARL) formula – that could be technically achieved for the system operating pressure, average service connection length and service connection density.

This message is supported by the European Union’s Good Practices on Leakage Management, which conforms to the IWA indicators. It also provides additional guidance on ‘Fit for Purpose’ performance indicators for differing operational objectives, and a footnote assists in choice of urban systems or rural systems.


The Fit for Purpose performance indicators are increasingly accepted within Europe and available to be used internationally as volumetric performance indicators for target-setting and tracking progress; the ILI for technical performance comparisons between systems; and the UARL as a measure ‘how low can you go’.

As water professionals we have a duty to reinforce earlier international messages, which have been discussed for more than three decades, that expressing real losses as the percentage of SIV gives a misleading perspective of true performance because it is strongly influenced by changes and differences in consumption, which may vary substantially seasonally and from one year to another, and is not under the control of the utility; it does not make allowance for any system-specific key factors (see second Table above); and gives misleading perspective of true performance.

Water Loss Control professionals have recently launched a new initiative aimed at ending the use of the percentage of SIV in the sector. Professionals abandon Percentages of SIV contains numerous international examples showing that using the percentage of SIV is a misleading performance indictor for leakage. Other water loss professionals are welcome to join over 120 practitioners from 22 countries already supporting for the initiative.

Together we can lead a movement that finally ends the use of percentage of SIV as an indicator of a water utility’s performance.




This and many other topical issues will be debated during the Water Loss Europe 2017 conference, taking place in Copenhagen 06-07 September 2017 with the support of the IWA Water Loss Specialist Group.


Cor Merks, Allan Lambert, Marco Fantozzi and Mark Shepherd