The efforts to establish consistent specifications for water meters on European and international level have lead to a revision of the series EN 14154 "Water meters", ISO 4064 "Measurement of water flow in fully charged closed conduits - Meters for cold potable water and hot water" and OIML R 49 "Water meters intended for the metering of cold potable water and hot water". The results are summarised in the framework of the EN ISO 4064 standard series, "Water meters for cold potable water and hot water". This consists of the following parts: - Part 1: "Metrological and technical requirements"; - Part 2: "Test methods"; - Part 3: "Test report format"; Part 4: "Non-metrological requirements not covered in ISO 4064-1"; Part 5: "Installation requirements". For this purpose, Part 1 specifies the conditions water meters have to meet in order to comply with the legal metrology requirements of the countries in which water meters are subject to governmental supervision. This European standard also applies to water meters based on electrical or electronic principles and to water meters based on mechanical principles incorporating electronic devices, used to measure the flow volume of hot water and cold potable water. It also applies to electronic ancillary devices. Ancillary devices are optional. However, it is possible for national or international regulations to render some ancillary devices mandatory in relation to the utilization of water meters. The European Standard has been prepared by a Joint Working Group of ISO/TC 30/SC 7 "Volume methods including water meters" (secretariat: BSI, United Kingdom) and OIML TC 8/SC 5 "Water meters" (secretariat: BSI, United Kingdom) in collaboration with CEN/TC 92 (secretariat: SNV, Switzerland). The responsible German committee is NA 119-04-08 AA "Wasserzähler" ("Water meters") of the Water Practice Standards Committee (NAW).