Measuring Rainwater Tank Size

WATER | Alternative Water Sources | Rainwater

BASIX requires the applicant to enter in the rainwater tank size. It is recommended that the available rainwater storage is kept to a maximum by installing any drinking water supply top-up valves within 300mm from the base of the tank. If you require a greater top-up level, it is recommended that this volume is provided in addition to the size nominated in your BASIX commitments.

Local council authorities may require rainwater storage tanks for the sole purpose of fire fighting. This cannot be included in BASIX. The rainwater tank size nominated in BASIX must be in addition to this requirement.

When determining the size of a rainwater tank the following considerations should be made.

What needs to be considered   Appropriate action
 Roof area
  • Rainwater for irrigation, toilets and washing machines can be harvested from most roof materials. Consideration should be made to the type of paint used on roofs as lead based paints should not be used for rainwater harvesting.
  • Before selecting a rainwater tank it is important to work out how much roof area can realistically be connected to the tank.
  • A conceptual roof drainage plan should be prepared to identify the locations of ridges, gullies, gutter high points and optimal downpipe locations.
  • The larger the connected roof area, the greater the potential for capturing rainwater.
  • Roof areas should be kept clear of overhanging vegetation and tree branches to minimise the quantity of leaves falling on the roof and restrict access by animals including rodents, cats and possums.
Available Land Size
  • Consideration should be made to the land size available and the potential position for a tank, keep in mind required setbacks from fencing and adjacent windows.
Water Demand
  • Consider your total water demand based on the potential uses for the captured rainwater:

    • Irrigation
    • Laundry
    • Toilet Flushing
    • All hot water use
    • Drinking and household use
 
Local Rainfall
  • Use local rainfall data to help determine the rainwater capture potential of your rainwater harvesting system.

If you enter rainwater tank larger than a maximum allowable size, BASIX will advise you to consider the selection by not allowing certificates to be generated. Increasing the size of an already large tank may not result in proportionate improvements in potable water savings. It may be more cost effective to consider other water efficiency measures than increasing the rainwater tank indefinitely.

You can enter the maximum allowable size as advised by the BASIX tool, but still install a larger tank on site. Since the BASIX certificate states that "The applicant must install a rainwater tank of at least [number] litres on the site", the larger tank is regarded as over-complying with the BASIX requirement.

Material

There are a variety of rainwater tanks types available and due consideration should be made when selecting the appropriate tank type for each site.

  • Metal/Steel Tanks
  • Concrete Tanks
  • Plastic Tanks with Plastic Liners
  • Fibreglass Tanks
  • Bladders

If a rainwater tank will be located in a bushfire prone area, the tank should be fabricated from steel, concrete or other suitably protected material in accordance with NSW Rural Fire Service guidelines - NSW RFS website). Durability of other components should be confirmed with suppliers and appropriate warranties obtained for tanks and other system components.

Last updated: 22/09/2023