Technically, you need to ...
Published by Muhammad Alfalah Fauzi, CFD Engineer Intern at Institut für Wasserbau und Technische Hydromechanik (IWD) - TU Dresden
Technically, you need to consider the following factors in determining water meters which is also related to its accuracy and capability of measuring "real consumption":
The first is to determine your average/operating flowrate on your installation (commonly known as nominal flowrate or Q3). You need also logged data to know the flow profile of the installation, which flowrate consumes the most volume and spends most of the time.
The second is the Ratio (Q3/Q1), where Q3 is the average flow rate (operating flow rate) on the installation with +/- 2% of error margin and Q1 is the minimum flow to be measured by the water meters to be between +/- 5% of the error margin. Note that starting flow rate (Q start) is another point of measurement which is below Q1 with no error margin (could be more than +/- 5%) and not included in the metrological error of measurement. The bigger the Ratio (R), the better the measurement range and its capability to measure lower flowrate. For example, common mechanical meters have a Ratio (R) between R50 - R160, but current solid state meters could be up to R300 - R400 which is better to measure low flow rates.
The third one is the "Typical Error Curve". The typical error curve is unique for each meter which depends on the design, operating principle, materials, and many other technical factors. Here, you need to deeply analyze which flowrates operate the most and its typical error curve on that flowrate. For example, if 99% of your consumption is resulted by flowrate on Q3, then you need to find a meter with near-zero percent error on Q3 (or adjust the measurement to near-zero percent of error because some meters allow you to adjust the measurement).
Last but not least, current solid state meters (ultrasonic, electromagnetic) have enhanced their capability of measuring constantly near zero percent (+ 0.2% for example) which means the meter error is constantly between + 0.2% between all flowrates (no undulation of typical error curve like mechanical type meters).