Roof runoff: Maximising its use

Although roof runoff may not always meet bacteriological quality for drinking water, it is, nevertheless, suitable for a range of other household and commercial uses, particularly with water quality improvement and disinfection devices. A spreadsheet has been developed for users to estimate their tank size from rainfall and connected roof area, for a range of demand patterns, including irrigation and seasonal occupation using the water balance equation. It is found that about 65% of rainfall is potentially harvestable with common tank sizes. The cost of rainwater tanks based solely on their water supply is not competitive with many reticulated supplies, and consideration needs to be given to the many multiple benefits.