In many developed countries water meters are used to measure the volume of water used by residential and commercial building that are supplied with water by a public water supply system. Water meters can also be used at the water source, well, or throughout a water system to determine flow through a particular portion of the system. In most of the world water meters measure flow in cubic metres (m3) or litres but in the USA and some other countries water meters are calibrated in cubic feet or US gallons on a mechanical or electronic register. Some electronic meter registers can display rate-of-flow in addition to total usage.
There are several types of water meters in common use. The choice depends on the flow measurement method, the type of end user, the required flow rates, and accuracy requirements.
In North America, standards for manufacturing water meters are set by the American Water Works Association.