Rainwater tanks in the urban environment - Friend or foe?

The harvesting of rainwater is preached as sustainability in all cases. This paper addresses the issues associated with installing rainwater tanks in the urban environment as a supplement to a reticulated supply. The results of modeling of rainfall and water demand on a household basis are presented complete with the assumptions and limitations of the modeling. The assumed variables are adjusted to examine the effects on the sustainability of the supply throughout the year.

This paper challenges the widely held belief that rainwater tanks are sustainable and always:

• Reduce the demand on the reticulated supply.
• Conserve natural resources.
• Reduce the consumers costs

This paper demonstrates that the installation of rainwater tanks for supplementary water supply is not a cost effective proposition and offers no benefits to the size of the water treatment plant and water supply network. Economic and environmental benefits may be achieved in delaying future water sources if the current water source is stored water (dam, lake, aquifer, etc.). However, if the source is a river, then any environmental or economic benefit is at best marginal.