The volume meter method records the initial and final readings of a totalizing water meter over a measured elapsed time. The difference in readings gives the volume consumed during the test interval. Dividing by the elapsed time (converted to hours) yields the average flow rate, which is then multiplied by the annual operating hours to obtain total annual water consumption.

\begin{equation}\label{eq:water-reduction-volume-meter} W_{use} = \frac{(V_{final} - V_{initial}) \cdot 60}{t_{elapsed}} \cdot t_{op}\end{equation}

Symbols

\(W_{use}\)	Annual water use \([\unit{ \gallon\per\year}]\)
\(V_{final}\)	Final meter reading \([\unit{ \gallon}]\)
\(V_{initial}\)	Initial meter reading \([\unit{ \gallon}]\)
\(t_{elapsed}\)	Elapsed time of measurement interval \([\unit{ \minute}]\)
\(60\)	Conversion factor from minutes to hours \([\unit{ \minute\per\hour}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)