Regardless of the measurement method used to determine annual water use, the annual water cost is obtained by multiplying the water use by the cost per unit volume of water. This formula applies uniformly to the metered flow, volume meter, bucket, and other methods.

\begin{equation}\label{eq:water-reduction-water-cost} C_{water} = r_{water} \cdot W_{use}\end{equation}

Symbols

\(C_{water}\)	Annual water cost \([\unit{ \dollar\per\year}]\)
\(r_{water}\)	Water cost rate \([\unit{ \dollar\per\gallon}]\)
\(W_{use}\)	Annual water use \([\unit{ \gallon\per\year}]\)