Guidance on use of rainwater tanks

2. Uses of rainwater

Page last updated: March 2011

Rainwater tanks have historically been used as an essential means of supplying drinking water in many rural and remote parts of Australia. The location, style, construction and use of rainwater tanks have changed significantly over time.

There has been a steady and acceptable progression from rainwater being used in urban areas for irrigation to its modern use in a dual household reticulation system complete with associated controls to prevent backflow or contamination of the high quality regulated mains supply. The use of rainwater tanks is increasing as communities adjust to the reality of life with water restrictions and drought.

While the use of rainwater tanks in urban areas has previously been debated, it is now strongly encouraged by all levels of government and supported by some with offers of rebate. The Australian Government offers a significant rebate on the installation of a rainwater tank under the long term Water for the Future Plan and the associated National Rainwater and Greywater Initiative. Other rebates are provided from time to time in various states/territories and regions.

The use of rainwater tanks has become a major strategy to enhance water conservation, reduce the burden of water restrictions and address the increasingly dramatic impacts of drought and climate change. Rainwater tanks now provide for a multitude of uses, including:

  • drinking water
  • garden watering
  • toilet flushing
  • laundry usage
  • replenishing domestic pools or spas
  • car washing
  • supplying the hot water system
  • thermal buffers to insulate houses
  • ventilation for buildings
  • protecting homes from bushfires.
While there is versatility in the uses of rainwater, there is also a corresponding risk. Microbiological quality is not as reliable as high quality mains water, particularly after rain events that follow long dry spells. The risk of contracting illness from rainwater supplied from well-maintained roof catchments and tanks is very low, although it should be noted that the risk increases with less maintenance and cleaning, and in the absence of a first flush diverter. If in doubt about the microbiological quality of rainwater, the water should be either disinfected or boiled prior to use.

There are also a number of chemical risks associated with rainwater. For example, impacts from major industrial emissions, such as lead in Port Pirie, may result in tank rainwater not being suitable for drinking and food preparation by particular vulnerable groups, such as pregnant or breastfeeding women and young children. Refer to local health authorities for further advice.

The water quality requirements for non-potable uses of rainwater are lower than those for drinking water, while higher quality water may be required for some medical procedures, such as kidney dialysis.Top of Page

The Australian Guidelines for Water Recycling: Managing Health and Environmental Risks 2008 provide an assessment of the likely risks associated with the intended use and exposures for alternative water supplies. If there are concerns about the risks associated with the end use of rainwater the default values established in the above national guidelines can be used to establish microbial and chemical risks through ingestion and frequency factors. Consumption or ingestion from showering is generally less than 100 mL per day, while ingestion associated with laundry use is estimated at 0.1 mL at 100 times per year, and toilet flushing is estimated at 0.1 mL at 1100 times per year, with gardening much lower. It should be noted that aerosol volumes are less for activities inside the house than those produced by garden irrigation. Risks associated with the use of rainwater for drinking are higher because of the volumes of water consumed. Guideline values cited in the ADWG are based on a daily consumption of 2 L of water per day for an adult and 1 L for a child.

The use of rainwater to supply hot water services has attracted increasing interest as the hot water infrastructure is already a separate supply. Rainwater may cause corrosion in water heating systems and advice should be sought from suppliers on the use of rainwater in these devices. It not recommended that water from the hot water tap be used for drinking or cooking. Other uses of hot water in the home result in lower exposures and therefore less risk from microbial or chemical contamination.