Non revenue water (NRW) is water that has been produced and is lost before it reaches the customer. Losses can be real losses (through leaks, sometimes also referred to as physical losses) or apparent losses (for example through theft or metering inaccuracies). High levels of NRW are detrimental to the financial viability of water utilities, as well to the quality of water itself. NRW is typically measured as the volume of water "lost" as a share of net water produced. However, it is sometimes also expressed as the volume of water lost per km of water distribution network per day.

Breakdown of NRW into its components

The International Water Association (IWA) has developed a detailed methodology to assess the various components of NRW. Accordingly NRW has the following components:

• Unbilled authorized consumption
• Apparent losses (water theft and metering inaccuracies)
• Real losses

In many utilities the exact breakdown of NRW components is simply not known, making it difficult to decide about the best course of action to reduce NRW. Metering of water use at the level of production (wells, bulk water supply), at key points in the distribution network and for consumers is essential to estimate levels of NRW.