The Association has documented a Position Paper that highlights the triple benefit of rainwater harvesting:
• Rainwater harvesting reduces the costs of water infrastructure across the urban system
• Rainwater harvesting water-efficient appliances reduce household expenditure on water
• Rainwater harvesting reduces stormwater management costs.
The Position Paper outlines how significant rainwater harvesting is in Australia, how rainwater harvesting works and what the future holds. The Position Paper concludes there is no doubt rainwater harvesting will be a major water policy issue in Australia in the 21st century.
Rainwater Harvesting Position Summary
Based on the research of Professor PJ Coombes
What is Rainwater Harvesting and why is it important?
Rainwater Harvesting is rainwater captured from a roof into a container. Rainwater Harvesting has a triple benefit in urban areas:
- Rainwater harvesting reduces the costs of water infrastructure across the urban system
- Rainwater harvesting with water-efficient appliances reduces household expenditure on water
- Rainwater harvesting reduces stormwater management costs.
How important is Rainwater Harvesting?
Rainwater Harvesting is the third largest source of water in Australia, after surface water (dams) and groundwater. Rainwater Harvesting provides an independent estimate of 274 billion litres annually. According to the ABS one in four, or 26% of Australian houses have a rainwater tank. The ABS estimate rainwater provides 177 billion litres, or 9% of residential water in Australia worth $540 million. Outside of urban areas rainwater provides 63% of residential water or 109 billion litres.
- Rainwater harvesting is the first and most efficient element of an integrated water management system.
- Because rainwater falls on roofs it is a local supply that can be collected where it is needed
- Because rainwater is usually high quality it can meet significant local water demand until it runs out.
- Capturing rainwater reduces the negative impacts of urban water on natural catchments.
- Coombes and Smit estimated savings from rainwater harvesting and water efficient appliances in 2016 in Sydney alone of 90 billion litres annually, equivalent to the entire capacity of the Sydney $1.8B desalination plant.
Rainwater Harvesting is the most accessible source of water in Australia. All urban areas continue to enjoy rainfall even in a drought, however, rainwater harvesting continues to provide water long after natural catchments become too dry for stream runoff. Desalinated water is not dependent on natural rainfall but it does rely on an electricity network, water distribution system and high levels of public expenditure.
How does Rainwater Harvesting work?
Rainwater Harvesting is a system with interacting elements including rain, roof and collection, tank, pump and rainwater uses.
- Using efficient water use appliances (such as front loading clothes washers, low flow showers and low flush toilets) within the house will reduce the capital and operating costs of the system.
- The risk of becoming ill from rainwater harvested water is low. Three million Australians rely entirely on rainwater2 and there is no evidence of widespread health impacts. A rainwater harvesting system has a natural treatment train that addresses many contaminants and other water quality issues are straightforward to manage. A mains water system is recommended for drinking water if it is available.
- Rainwater Harvesting is cost effective. A 5000-litre residential tank with pump and plumbing can easily be installed for $3000. Coombes research indicates that annual savings of 90kl each year can be achieved from rainwater harvesting and water efficient appliances7.
- Urban areas create excess stormwater because they are dominated by impervious surfaces which create large amounts of runoff. This excess runoff leads to dangerous flooding and environmentally damage by reducing water quality in the natural environment. Rainwater harvesting reduces the peak, volume and level of contaminants of urban stormwater.
What is the future of Rainwater Harvesting?
Rainwater Harvesting combined with access to mains water is a cost-efficient supply of water in Australia with savings to householders and downstream stormwater benefits.
- Rainwater harvesting reduces the peak demand and overall demand for mains water reducing future demand for water infrastructure at every scale.
- The system wide savings from water infrastructure and stormwater infrastructure and household savings from a rainwater harvesting system on every house would save Victorians $6B and South East Queensland $3.5B by 20507.
- There is no doubt rainwater harvesting will be a major water policy issue in Australia in the 21st century.
 Peter Coombes, based on purchased ABS data, 2016
 ABS (2013), Environmental Issues Water Use and Conservation
 ABS (2016), Water Account Australia 2014-15
 Coombes and Smit (2017), Greater Melbourne Alternative Water Plan
 Coombes P. J., and Barry M. E., (2008), The relative efficiency of water supply catchments and rainwater tanks in cities subject to variable climate and the potential for climate change, Australian Journal of Water Resources, 12 85-100
 UWCS and RHAA (2017) Design Specification for Residential Rainwater Harvesting
 Coombes P.J., Smit M., and MacDonald G., (2016), Resolving boundary conditions in economic analysis of distributed solutions for water cycle management. Australian Journal of Water Resources, Vol 20, 11-29.
 Coombes P. J., Smit M., Byrne J., and Walsh C., (2016) Stormwater, waterway benefits and water resources benefits of water conservation measures for Australian cities. HWRS 2016, Engineers Australia, Queenstown, New Zealand.
 Bonacci Water (2011) Living Melbourne, Living Victoria Greater Melbourne Systems Model – Modelling in support of Living Victoria Ministerial Advisory Council