Rainwater Tanks
What it is
Rainwater tanks can store runoff from your roof for garden watering. They can make an important contribution towards reducing the residential water supply demand and are a valuable water conservation measure. The ACT Government's Rainwater Tanks Guidelines provides comprehensive information on this subject.
What we are currently doing
Rainwater tanks are a major component of the ACT Government's Think water, act water strategy, as they can assist towards meeting our 25% target reduction of drinking water consumption per person by 2023.
The strategy recognises the increased benefits of installing a rainwater tank, in terms of water saving and stormwater reduction, when the tank water is used for internal purposes such as toilet flushing and clothes washing as well as garden watering. This provides a way for the tank water to replace the drinking water all year round.
The ACT Government has provided household rebates for the installation of rainwater tanks to assist the community contribute to water conservation. To be eligible for a rainwater tank rebate, the tank must be plumbed for some internal use, for example to the laundry or toilet.
Rainwater tanks are also a major component of the Water Sensitive Urban Design (WSUD) guidelines introduced by the ACT Government. The WSUD target for all new developments and re-developments is a 40% reduction in drinking water use.
The Think water, act water strategy states that the cost to install rainwater tanks to existing households (based on a 200 square metre house, with the entire roof connected to a tank and plumbed to the toilet and laundry) would translate into about $4 per kilolitre (kL) for fitting to existing houses. This is compared to the current highest cost of drinking water, being $1.74/kL plus the ACT Government's $0.55/kL Water Abstraction Charge.
The Rainwater Tanks Guidelines states that a rainwater tank connected to a building with a 150 square metre roof can provide up to 90KL of water per year (assuming the tank water is used for garden, toilet and laundry).
Issues with this option
Assuming a cost of $5,000 - $10,000 per property for over 90,000 houses, it is estimated that the cost for installing a tank in all households would be in the region of $450 million to $900 million for 8 gigalitres per year.
This cost would be met up front by today's generation (assuming the property owner or ACT Government did not borrow to fund the works).
The time required to implement these rainwater tank systems in all households would be many years, based on the limited supply of rainwater tanks, limited availability of plumbers and drainers for installation, and the logistics of fitting systems to approximately 90,000 semi-detached residential properties. The Think Water, act water strategy is however looking at ways to accelerate the uptake of rainwater tanks through an expansion of it's rebate scheme with mandatory installation in all newly developed suburbs.
Rainwater tanks need to be continually managed by ongoing monitoring and regular maintenance, to avoid health issues. They are also dependent on rainfall which in the ACT is irregular and inconsistent, reducing the benefit of rainwater tanks during drought periods.
Based on this, there is limited opportunity (in the short term) for city-wide rainwater tank use at levels above what is already being put in place.
Although rainwater tanks are expensive to install and dependent on rainfall, they represent a valuable long term means to reduce our dependence on mains water.