The Urban Water Security Research Alliance (the Alliance) has undertaken an integrated research program to inform the effective design and management of rainwater tank systems, helping to ensure that their potential benefits are realised.

With Australia’s variable climate and vast areas of low population density, the use of rainwater tanks has long been a common and wellestablished practice across the country, particularly in rural and remote areas that do not have access to a mains water supply.

As urbanisation increased, rainwater tanks suffered a drop in popularity, largely due to concerns about health risks associated with mosquito breeding. However, with increasing demand for water in our cities coupled with decreasing supplies due to long-term drought conditions and the resultant widespread water restrictions, an opportunity to utilise rainwater tanks for non-drinking purposes in urban areas arose.

This opportunity has been recognised by the Australian Government, as well as many State, Territory and Local Governments, with policies and rebates encouraging rainwater tank installation. For example, in South-East Queensland (SEQ), rainwater tanks have become an integral part of the strategy to manage water supply and demand. The State and many Local Governments have provided rebates for tank installation. In addition, in 2007, during one of the worst droughts in the region’s history, the Queensland Government introduced legislation around mandatory water savings targets for all new Class 1 (residential) buildings as part of the Queensland Development Code. The most common method for achieving these targets has been to install a rainwater tank that is internally plumbed into the household’s laundry cold water tap, toilet and outdoor taps. The SEQ Water Strategy recognises the value of rainwater tanks in providing an alternative local water supply that reduces demand on the SEQ Water Grid.

To maximise on-going benefi ts from the considerable national investment in rainwater tanks, continued growth in our knowledge of the performance, reliability, management, and community attitudes towards rainwater tanks in the urban environment will be vital.

Research outcomes to date

The Alliance has addressed many of the research needs associated with rainwater tanks. This multi-disciplinary research has provided increased understanding for improved rainwater tank design and management, and has highlighted areas where further investigation has the potential to deliver the greatest benefits.

Water savings

It is widely agreed that rainwater tanks have the potential to save considerable amounts of mains water; however, the exact water savings that can be expected can be difficult to predict. Alliance research used 2009 and 2010 water billing information to examine water savings in households with internally plumbed tanks across SEQ. The average mains water saving was found to be approximately 58 kilolitres per household per year or 50 litres per person per day (roughly one bath tub of water per household per day). This is equivalent to 34 per cent of the average total mains water used by households in SEQ. Preliminary results from a physical inspection of the setup of a number of tank systems has indicated that further savings could be achieved by increasing the roof area connected to the tank, which in 85 per cent of the systems assessed, is below the minimum requirement of 100m² of connected roof area. These results demonstrate that rainwater tanks are effective in achieving significant water savings and will help inform future water portfolio planning by enabling more accurate forecasting of the water savings that rainwater tanks can provide.

Energy efficiency

Previous research has suggested that rainwater tanks are considerably less energy efficient than the traditional water supply. To investigate this, Alliance researchers  analysed water flow characteristics and operations of rainwater tank pumps in a controlled model house setting to understand factors that impact energy usage. They concluded that the most commonly used pumps are efficient for high-flow applications, such as watering the garden, but much less efficient for low-flow applications, such as toilet flushing and the washing machine. As pumps are often operating in their low efficiency range, this suggests that there is considerable potential to improve energy efficiency of pump systems. Research results indicated that correct pump sizing and informed selection of system components could significantly improve energy efficiency to less than 1.5 kilowatt hours per kilolitre of water. This is lower than the energy footprint of other alternative water sources, such as desalination and recycled water, an important consideration in the selection of options for sustainable urban water supply. This research has demonstrated that energy efficient systems can be achieved; the next step will be to incorporate this knowledge into the development of system configuration or installation guidelines for tank owners.

Tank maintenance

Water savings and energy efficiency are not only influenced by system design but also by system management, making this an important  consideration in achieving  maximum benefits from rainwater tanks over the long-term. Alliance researchers conducted a series of surveys to provide insights into the way people in SEQ manage and maintain their tanks. The research showed a small but significant difference in the maintenance habits between owners of mandated tanks when compared with owners who voluntarily retrofitted their tanks. Retrofitters were more self-motivated towards rainwater tank maintenance and were keen to learn more to ensure the longevity of their tank. Conversely, owners of mandated tanks felt that they didn’t know enough about maintenance, and were less willing to find out more or undertake the required maintenance behaviours. These results are of concern as a lack of maintenance could lead to faster tank deterioration and diminished return on investment.

Tank owner and non-owner attitudes

Research into the attitudes of rainwater tank owners and non-owners in SEQ found that participants were more likely to install a rainwater tank if a severe water shortage occurred, or if they believed they could be vulnerable to water shortages. Conversely, reasons for not having a tank included lack of space, cost, mistrust in authorities and those governing water, or a belief that water shortages were no longer a threat in SEQ. Encouragingly, most tank owners were happy with their system, however, this was strongly dependant on how well the system had been designed and installed, and how competent owners felt in managing their tank. These and the findings around tank maintenance suggest that greater information and guidance is needed following tank installation. By increasing hands-on tank knowledge and skills, education programs have the potential to improve maintenance behaviours and owner-satisfaction as a result of owners feeling more engaged and competent in the management of their tank. However, alternative options for providing rainwater tank services to home owners also need to be explored, as these may more be effective in maximising efficiency and lifecycle benefits.

Health risks

Alliance research has also investigated the potential health risks associated with the use of water from rainwater tanks. Analysis of samples from 80 rainwater tanks from across SEQ showed that 71 per cent of tanks did not meet Australian Drinking Water Guidelines due to the presence of Eschischeria coli (E. coli). Some samples were also found to be positive for pathogens and further research is currently underway to determine whether these pathogens are active, with the potential to cause infection. As E.coli is present in animal faecal matter, these results are not surprising considering the high incidence of possums and birds on urban roofs. The results reinforce government recommendations that, where mains water is available, water from rainwater tanks should only be used for non-drinking purposes unless  adequately treated. This research will help guide the development of transparent, accurate and valid policies and guidelines for the treatment and use of water from rainwater tanks.

Communal rainwater tank systems

Communal rainwater tank systems could be used to address owner maintenance issues and potential health risks. To better understand these systems, Alliance  researchers investigated a communal rainwater system in SEQ. The system is currently delivering 37 kilolitres of harvested rainwater per household per year based on local conditions. Researchers are now looking at the management model and community perceptions associated with this system. These findings will help determine how to maximise efficiency of communal tank systems as a useful option for rainwater harvesting.

Future research opportunities

The significant body of integrated research undertaken by the Alliance has provided answers to a wide range of questions around rainwater tanks. However, this research has also highlighted opportunities where further investigation would provide valuable insights.

Maximising mains water savings - What changes would need to be made to individual and communal rainwater tank systems and policies to reach their full water savings potential?

Minimising energy use – What are the optimal tank designs for different housing configurations, and how can these best be implemented to maximise energy efficiency?

Managing health risks – Further research is required to better understand how processes such as sunlight and natural biota can reduce the health risk of pathogens in rainwater tanks. This will help inform guidelines for appropriate treatment and the potential for wider use of rainwater, for example in showers.

Optimising the longevity of tank infrastructure – Very little is known about the existing condition of urban rainwater tanks, their likely lifespan and how this may be affected by tank maintenance. Research aimed at enhancing owner awareness and improved tank operation and maintenance programs, including the owners’ willingness to pay for such a service, would help ensure the longer-term benefits from the investment in rainwater tanks.

Exploring options for roof water supply services – Many of the above issues may be better managed through alternative roof water supply service models. Research is needed to investigate and inform the design of effective service models that deliver social, environmental, and economic benefits.

Following through on these research opportunities would not only help ensure that Australian communities derive maximum water supply benefits and return on investment in rainwater tanks, but could also help position the country as a world-leader in rainwater tank design, management and service provision.

The Urban Water Security Research Alliance

The Urban Water Security Research Alliance (UWSRA) is leading water research and security in South East Queensland through a $50 million, five-year partnership between the Queensland Government, CSIRO’s Water for a Health Country National Research Flagship, The University of Queensland and Griffith University.

UWSRA is addressing South East Queensland’s urban water issues through targeted, multidisciplinary research into water security, including recycled water, rainwater and stormwater. It is Australia’s largest, regionally focused urban water research program, contributing to a national effort to research water solutions for Australia.

Further information

More detail on the above research can be found in a number of publications at www.urbanwateralliance.org.au/publications.html

Contact details box:
Don Begbie
Alliance Director
Ph: +61 7 3247 3006
Fax: +61 7 3405 0373
Don.Begbie@qwc.qld.gov.au