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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. == NRW components and audits== The International Water Association (IWA) has developed a detailed methodology to assess the various components of NRW. Accordingly, NRW has the following components:〔International Water Association:(), August 2003, accessed on November 29, 2009〕 * Unbilled authorized consumption * Apparent losses (water theft and metering inaccuracies) * Real losses (from transmission mains, storage facilities, distribution mains or service connections) In many utilities the exact breakdown of NRW components and sub-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 (see Water metering). In most developed countries, there are no or very limited apparent losses. For developing countries the World Bank has estimated that, on average, apparent losses - in particular theft through illegal connections - account for about 40% of NRW.〔World Bank, December 2006: (The Challenge of Reducing Non-Revenue Water in Developing Countries ), p. 3〕 In some cities, apparent losses can be higher than real losses. Reducing apparent losses from illegal connections is often beyond what a utility can achieve by itself, because it requires a high level of political support. Illegal connections are often in slums, which means that their regularization in some cases particularly affects the poor. A water audit is a key tool to assess the breakdown of NRW and to develop a program for NRW reduction. Often a distinction is made between unvalidated and validated water audits.〔American Waterworks Association:Water Wiser:(Water Audits and Loss Control ), accessed on November 8, 2009〕〔Johnson, Paul V.: (Unaccounted-for water puzzle: More than just leakage ). Florida Water Resources Journal, February 1996〕 Unvalidated water audits are desktop studies that include many estimates and their results can have an error range for real losses of +/- 50% or more. Its main value is to identify where it is necessary to reduce the uncertainty of the water audit through validation. Validating water audits is a complex process that involves testing of production water meters, testing of a representative random sample of customer meters, eliminating systematic errors created through the billing process and validating the number of illegal connections through aerial mapping, field surveys or cross-references between various existing databases.〔Paul Fanner:Driving down water loss:validating water audits for accurate NRW management, in:Water 21, Magazine of the International Water Association, December 2009, p. 53-54〕 In developing countries it is rare to find utilities that have undertaken validated water audits, and even in developed countries they are not systematically used. The American Water Works Association (AWWA) has developed Water Audit Software which allows utilities to rate the overall degree of validity of their water audit data. Guidance on loss control planning is given based upon the credibility of the data and the measure of losses displayed by the water audit.〔American Water Works Association:(Water Loss Control ), retrieved on May 2, 2013〕〔American Water Works Association:(M36: Water Audits & Loss Control Programs manual, Third Edition ), retrieved on May 2, 2013〕 NRW is sometimes also referred to as unaccounted-for water (UFW). While the two terms are similar, they are not identical, since non-revenue water includes authorized unbilled consumption (e.g. for firefighting or, in some countries, for use by religious institutions) while unaccounted-for water excludes it.〔International Benchmarking Network for Water and Sanitation(IB-NET): (Non-Revenue Water at the International Benchmarking Network for Water and Sanitation Utilities (IB-NET) )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Non-revenue water」の詳細全文を読む スポンサード リンク
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