Water meter is normally for measuring water used volume of household and factory, which are supplied with water by a governmental water board.
Most of water meters measure water used volume in the unit of cubic metres (m3) or litres but in the USA and some other countries water meters are calibrated in cubic feet or US gallons.
Many countries have their own requirements on water meters. Like in the European countries, water meter complies with EN14154; in China, water meter complies with GB 778; and so on. But normally these will refer to several international standards, like ISO4064, and OIML R49.
For different models, water meter could be divided intodisplacement and velocity. And common displacement includes oscillating piston and nutating disc meters. Velocity includes single-jet water meter, multi-jet water meters, and turbine water meters. But all of them, we also call mechanical water meters.
And, there are also the designs of non-mechanical, like electromagnetic water meter, ultrasonic water meter, and other water meters for some kinds of special uses.
Besides, with the development of data communication technology, it combines with tradtional mechnical water meter or new technology water meter into new function water meter. For example electro-mechanical water meters, like prepaid water meters and automatic meter reading water meters (eed switch, hall or photoelectric coding register as the signal output). And then people collect data and send data by different ways, like Radio frequency (eg. Lora), GPRS, M-bus, RS485, and etc.