(Also known as a water tank, rain barrel or water butt)
What is a rainwater tank: A rainwater tank is a water storage tank that collects and stores rainwater runoff. This runoff is typically collected from all or part of the roof and can be utilised around the home to reduce demand on “town” water.
Rainwater tanks are not considered an effective flood risk management measures. Why? A rainwater tank usually provides little storage. For example 10mm of rain over a 200 square metres of roof or 20mm over a 100 square metres of roof, would add 2 cubic metres or 2000 L to a tank. During a flood, rainfall would typically exceed the tanks capacity very early, limiting its ability to reduce down-stream flood flows. It is possible however, that rainwater tanks may retard some floodwater, reducing the peak flow at some localised sites but in general rainwater tanks should not be considered a flood risk management measure (DECC, 2007).
DECC (2007). Rain Water Tanks- Limitations as FRM Devices. NSW Department of Environment and Climate Change. Access on 3/05/2013 at: http://www.environment.nsw.gov.au/resources/floodplains/FRMGuidelineRainwaterTanks.pdf