Water Meter Accuracy Measurment

How is the accuracy of water meters tested? Was it proven or is it convenient for utilities to adopt the volumetric meters and retain the inferential meters which are simple and cheap instead of the expensive meters which show the real consumption? The idea of equability is that volumetric meters (oscillating piston and nutating disc) and the inferential meters (single jet and multi-jet) will show a registered consumption that is not the true consumption but that by the equable measurement. The registered consumption can be used as a proxy for the true consumption without any consumers being significantly advantaged or disadvantaged by the reading. For example, if the meter registers 100 m3 then the unregistered consumption may be 5 m3 and it will be, within acceptable limits, the same 5 m3 unregistered consumption for all consumers.