The metered flow method uses the instantaneous flow rate reported by a water meter together with the annual operating hours to obtain total annual water consumption. The factor of 60 converts the meter reading from gallons per minute to gallons per hour before multiplying by the annual operating hours.

\begin{equation}\label{eq:water-reduction-metered-flow} W_{use} = \dot{V}_{meter} \cdot 60 \cdot t_{op}\end{equation}

Symbols

\(W_{use}\)	Annual water use \([\unit{ \gallon\per\year}]\)
\(\dot{V}_{meter}\)	Meter reading (instantaneous flow rate) \([\unit{ \gallon\per\minute}]\)
\(60\)	Conversion factor from minutes to hours \([\unit{ \minute\per\hour}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)