The key to developing a strategy for management of non-revenue water (NRW) is to gain a better understanding of the reasons for NRW and the factors which influence its components. Then techniques and procedures can be developed, and tailored to the specific characteristics of the network and local influencing factors, to tackle each of the components in order of priority. This diagnostic approach, followed by the practical implementation of solutions which are practicable and achievable, can be applied to any water company, anywhere in the world, to develop a strategy for NRW management.

The first step in developing a strategy is to ask some questions about the network characteristics and the operating practices, and then use the available tools and mechanisms to suggest appropriate solutions, which are used to formulate the strategy. Typical questions are:

• How much water is being lost?
• Where is it being lost from?
• Why is it being lost?
• What strategies can be introduced to reduce losses and improve performance?
• How can we maintain the strategy and sustain the achievements gained?

The components of NRW can be determined by conducting a water balance. This is based on the measurement or estimation of water produced, imported, exported, consumed or lost – the calculation should balance. The water balance calculation provides a guide to how much is lost as leakage from the network (`real` losses), and how much is due to `apparent` or non-physical losses

Because of the wide diversity of formats and definitions used for water balance calculations internationally (often within the same country), there has been an urgent need for a common international terminology. Drawing on the best practice from many countries, the IWA Task Force on Water Losses has produced an international best practice approach for water balance calculations, including definitions of its components, and for comparing performance between utility operators.

The paper describes the IWA approach to developing a NRW strategy, a water balance calculation, and an international measure of performance - the international leakage index (ILI).