When using the AWWA Water Audit software for flow weighted average you will find one input location for master meter and supply error adjustments for each of the following: volume from own sources, water imported and water exported. If you have more than one master meter for any of these three, you will need to calculate the flow weighted average meter error. This tool assists you with these calculations. You only need to input the total flow and meter error for each meter. The flow weighted average is then calculated for you and this number can be entered into the AWWA Water Audit software.
Source: EFC at UNM