ISO 4064-5:2014 applies to water meters used to meter the volume of cold potable water and hot water flowing through a fully charged, closed conduit. These water meters incorporate devices which indicate the integrated volume. ISO 4064-5:2014 specifies criteria for the selection of single, combination and concentric water meters, associated fittings, installation, special requirements for meters, and the first operation of new or repaired meters to ensure accurate constant measurement and reliable reading of the meter. In addition to meters based on mechanical principles, ISO 4064-5:2014 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 volume of cold potable water and hot water. It also applies to electronic ancillary devices. Ancillary devices are optional. However, national or international regulations may make some ancillary devices mandatory in relation to the utilization of the water meter. The recommendations of ISO 4064-5:2014 apply to water meters, irrespective of technology, defined as integrating measuring instruments continuously determining the volume of water flowing through them.