This document applies to water meters intended for residential, commercial, light industrial and industrial use, and specifies the requirements and certification procedures for water meters, irrespective of the design technologies used to meter the actual volume of clean cold potable water or heated water, flowing through a fully charged, closed conduit. These water meters shall incorporate devices, which indicate the integrated volume. This document also applies to water meters based on electrical or electronic principles, and to water meters based on mechanical principles incorporating electronic devices, used to meter the actual volume flow of cold potable water or heated water. It provides metrological requirements for electronic ancillary devices when they are subject to metrological control. As a rule the ancillary devices are optional. However national or international regulations make some ancillary devices mandatory in relation to the utilisation of the water meter.