Rainwater tanks supplement the bulk water supply
Less than 5% of domestic water is actually consumed for drinking. Toilet flushing, laundry and outdoor uses represent a significant portion of domestic water consumption but these do not require water to be treated to such a high standard. Such uses can be satisfactorily supplied from rainwater collected from roofs and stored in tanks.
Utilising rainwater for various uses (e.g. toilet flushing, garden watering and clothes washing) can result in water savings from the mains water supplies and large reductions in stormwater discharges, especially where the area of the roof catchment that supplies the tank(s) is maximised (e.g. between 80% and 100%)
It is often mistakenly assumed that using rainwater solely for outdoor uses such as watering the garden will produce substantial mains water savings. However mismatches between seasonal rainfall and outdoor water use patterns can result in poor use of rainwater, resulting in long periods during which the tanks are either empty or full.
To effectively supplement the bulk water supply, rainwater tanks need to be connected to water uses in the home (e.g. toilet, washing machine) so that water from the tank is used at a relatively constant rate and there is available space in the tank to capture water from the next rain event.
Rainwater tanks reduce drinking water use
The implementation of Council’s Demand Management Strategy has set a short-term residential water consumption target of 180 litres per person per day. One of the ways to achieve this target is to reduce the consumption of treated potable (drinking) water from the public water supply that is used for non-potable uses. Council is therefore encouraging the installation of rainwater tanks to provide non-potable water for outdoor uses, flushing toilets and washing machines.
For this approach to be as successful as possible customers are being encouraged to install the largest tank that they can, given factors such as initial cost, space and ongoing operating and maintenance costs.
A minimum tank size of 5000 litres with a minimum roof catchment area of 160 square metres is recommended for single dwellings. For duplexes, triplexes, multi-dwellings and other buildings, it is recommended that the rainwater tank volume be maximised with 80% to 90% of the roof area connected.
Rainwater tanks reduce the volume of urban stormwater discharged to creeks and streams in the catchment
Urban areas increase the amount of impervious surfaces (e.g. driveways, roads, paths, roofs) in a catchment. This impairs the catchment’s ability to absorb rainwater and results in larger volumes of runoff.
By retaining rainwater on-site, rainwater tanks reduce the volume of water discharged to creeks and streams in the catchment. This also reduces the velocity or energy of water entering creeks and streams, which in turn, reduces downstream scour, sedimentation and riparian vegetation removal.
By capturing and retaining rainwater, tanks lessen the amount, intensity and frequency of downstream stormwater runoff and thereby partially offset the adverse impacts of urbanisation.
Rainwater can provide an alternative source of water for the following:
- Toilet flushing
- Washing machine cold tap
- Garden taps
- Residential garden irrigation
- Washing cars
- Filling ornamental ponds
- Topping up swimming pools and spas
Where there is a reticulated drinking (potable) water supply available to the property, NSW Health does not recommend the use of rainwater for:
- Drinking
- Cooking or other kitchen purposes
- Personal washing, such as baths, showers, hand basins and bidets
Connection of the rainwater tank supply to the household hot water system is not recommended as hot water is generally used for potable uses within the home. Depending on the condition and the construction materials of the roof catchment and tank, connection to the hot water system may also increase the likelihood of scaling and fouling of the hot water heater.
The NSW Government’s State Environmental Planning Policy (SEPP) (Exempt and Complying Development Codes) 2008 sets out conditions under which rainwater tanks may be installed without the approval of Council. Rainwater tanks with a capacity of 10,000 litres or less do not require local Council approval provided they meet all of the conditions outlined in the SEPP.
The SEPP conditions vary for above ground and below ground tanks and also vary depending on the zoning of the land where the tank/s is/are to be installed. Different conditions apply for land that is zoned rural or environmental, educational establishments and installations in acid sulphate soils. Council’s Building and Environmental Health Unit (02 6670 2440) should be consulted to ascertain the SEPP and approval requirements if in doubt.
Please refer to our Rainwater Tanks in Urban Areas Policy available in the Downloads and Other Information section below for a full list of the SEPP conditions for above ground and below ground tanks.