Estimation of Water Balance and Water Losses in Water Utilities – Experiences from the Belgrade Waterworks

 Branislav Babić1, Aleksandar Djukić1


1 Faculty of Civil Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, Belgrade, Serbia


The paper provides a review of methods for estimation of water balance and water losses in water supply systems. Results of investigations of water losses in the Belgrade Waterworks are presented in the paper. It is concluded that in investigated areas significant water losses exist and further investigations are needed to determine more accurately water losses components

Keywords: water supply, water losses, performance indicators, minimum night flow method




For more than a decade, water utilities and municipalities have been implementing investigations and estimation of water balance in water supply systems. Water balance components presented in Table 1 were proposed by the International Water Association (IWA) Water Loss Task Force and are widely accepted by water utilities.


Table 1: The IWA ‘best practice’ water balance

System Input Volume (corrected for known errors)

Authorized Consumption

Billed Authorized Consumption

Billed Metered Consumption (including water  exported)

Revenue Water

Billed Unmetered Consumption

Unbilled Authorized Consumption

Unbilled Metered Consumption

Non-Revenue Water (NRW)

Unbilled Unmetered Consumption

Water Losses

Apparent Losses

Unauthorized  Consumption

Customer Metering Inaccuracies

Data Handling Errors

Real Losses

Leakage on Transmission and Distribution Mains

Leakage and Overflows at Utility’s Storage Tanks

Leakage on Service Connections up to point of Customer metering



According to IWA, water losses have two main components: apparent losses and real losses. Apparent losses is water that is consumed but is not properly measured, accounted or paid for. These losses cost utilities revenue and distort data on customer consumption patterns. Real losses are the physical losses of water from the distribution system, including leakage and storage overflows. These losses increase the water utility's production costs and stress water resources since they represent water that is extracted and treated but never reaches beneficial use.

Water losses and Unbilled authorized consumption makes the Non-Revenue Water (NRW). The main task for every water utility is to reduce NRW. The long-term financial and environmental benefits of implementing water loss control measures far outweigh the initial investment costs. It is not, however, economically feasible to eliminate all water losses and there is no universal recommendation on the acceptable economic level of water loss. Each water utility must evaluate data on investments and savings and derive conclusions on acceptable economic levels of water loss. In these calculations water losses shall always be expressed as value of money saved, as follows (AWWA, 2009):

  • ­Value of water from real losses are calculated by using marginal costs of water production, transport and distribution;
  • ­Since apparent losses represent unpaid water used by the consumers, they are valued by using the retail rate that a water supplier charges its customers.


The objective of this paper is to give the overview of widely accepted standards for performance evaluation of water utilities in the field of water leakage. The paper will also present some results of investigations performed in the Belgrade Waterworks (BWS) with the aim to establish standard procedures and the required level of needed information for the efficient operation and maintenance of a water supply network and the assessment of water balance and the type and quantity of water losses.