<p>Total cistern volume can be estimated by multiplying the depth of design storm the catchment area. 1 mm of rain over 1 m<sup>2</sup> results in 1 L of runoff. | <p>Total cistern volume can be estimated by multiplying the depth of design storm the catchment area. 1 mm of rain over 1 m<sup>2</sup> results in 1 L of runoff. |