1 mm of rain landing on 1 m<sup>2</sup> of roof top produces 1 litre of water to store. <br> So a 5 mm storm on a 75 m<sup>2</sup> roof would require 375 L of storage volume. <br> | 1 mm of rain landing on 1 m<sup>2</sup> of roof top produces 1 litre of water to store. <br> So a 5 mm storm on a 75 m<sup>2</sup> roof would require 375 L of storage volume. <br> |