ISO 4064-1:2005 specifies terminology, technical characteristics, metrological characteristics and pressure loss requirements for cold potable water and hot water meters. It applies to water meters that can withstand maximum admissible working pressures (MAP) at least 1 MPa (0,6 MPa for meters for use with pipe nominal diameters, DN at least 500 mm) and a maximum admissible temperature, MAT, for cold potable water meters of 30 ºC and for hot water meters up to 180 ºC, depending on class. ISO 4064-1:2005 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 and hot water. It also applies to electronic ancillary devices. Generally ancillary devices are optional. The specifications of ISO 4064-1:2005 apply to water meters, irrespective of technology, defined as integrating measuring instruments continuously determining the volume of water flowing through them.