What are Apparent losses (AL)? What does it consist of?

Whilst Real Losses refers to the physical water losses i.e. the water leakages in the water distribution network and storage facilities, Apparent Water Losses (AL) refer to water losses emerging from the “non-billed” consumption of water. Vermesch et al [1], defines AL as volumes of consumption that reach consumers but are not billed. A. Rizzo et al [2], categorize AL into the following four fundamental elements indicated in Figure 1.

Figure 1

1.     Meter under-registration consists of the inability of a revenue water meter to accurately measure flows, especially the lower flows. This tends to increase with time and as the meter degenerates.

2.     Water theft is easy to conceptualize and consists usually of bypasses to the water meter, illegal connections, or willful damage to the water meter.

3.     Meter-reading errors consist of mistaken, or intentionally incorrect, meter-reading mistakes.

4.     Water accounting errors consist of billing anomalies, such as computer-based estimations, that do not reflect actual consumption values.


In his study on developing the Best Practice for Reducing Commercial losses, Loupos et al [3], claims that whilst utility companies focus on reducing Real Losses, AL is often overlooked and this can lead AL to be higher in volume than Real Losses. Furthermore, in most cases, AL is often attributed to meter under-registration.



1.     Vermersch, M., Carteado, F., Rizzo, A., Johnson, E., Arregui, F., Lambert, A. 2016. Water Audit Component Analysis and Best Practices. Guidance Notes on Apparent Losses and Water Loss Reduction Planning, 29–31. Available online at: http://www.leakssuite.com/wp-content/uploads/2016/09/AL-Guidance-Note-Final-15th-Sep-2016.pdf (Accessed on 30 October 2017).

2.     Rizzo A., Vermersch, M., John, G., Micallef, G., and Pace, R. 2007. ‘Apparent Water Loss Control: The Way Forward’, IWA Water21 Journal, August.

3.     Loupos, K., Amditis, A., Bettin, A., Charalambous, S., Bazzurro, N., Fantozzi, M., Boubaker, A.,Beji, A., Gaber, A., Al Shafei, M., and Kounoudes, A. 2014.‘Cooperation Framework towards Efficient Water Resources Management–The AQUAKNIGHT Project’. Athens, Greece.