Water tanks and Building Design

Incorporating water tanks in construction design is frequently one of the more challenging facets of designing more environmentally friendly buildings. Large amounts of rainwater pose structural, space and aesthetic challenges. Luckily the rainwater harvesting industry has responded with a massive array of rainwater tank solutions including bespoke tanks which can be built to suit the plan and available space.

The golden rule for rainwater storage is that 1,000 litres of water steps 1m³ and weighs only 1 tonne. Thus 10,000 litres of rainwater requires at least 10 cubic metres of distance and also the place where tank is placed needs to have the ability to hold 10 tonnes.

Rainwater Tanks: Feature vs. Hidden

The first decision which will decide the very best water tank solution for your design is if you would like to make the water tank a feature or to conceal it from sight. If the water tank will be a feature of the design of buildings like the Melbourne city conference centre then it is most likely to function as a steel tank (most concur that steel tanks are better looking than plastic tanks) or a customisable tank that can be incorporated into the whole design. Examples of acceptable “feature” water tanks incorporate corrugated steel square, circular and slimline tanks or any form of tank that has an external framework that allows other endings to be applied to it.

Hidden Rainwater Tanks

If the decision is to conceal the water storage then the tank could be hidden underground (poly or concrete with a tank liner), within the building structure (typically concrete with a tank liner) or someplace outside the building where it is out of site (which may also be a tank “disguised” with exactly the same external finish as the interior design). Bigger places such as the Docklands Stadium in Melbourne would normally have a dedicated enclosed space to store these tanks so that they are out of sight.

The key Actions to integrating water storage in architectural and construction designs are:

  • Calculate just how much water is required
  • Calculate how much water could be harvested in the roof area (refer to the Australian Standards Handbook on Rainwater Tank Design and Installation (PDF) (3 Mb) for help on the best way to compute these numbers )
  • Decide if the water storage will be a feature or concealed
  • Contemplate the perfect tank alternative for your design based on the answers to the above questions. This rainwater tank selection table provides a list of hidden & feature tank options.
  • Determine where and exactly what primary rainwater filter is required (primarily first flush apparatus and / or filtering rain heads)
  • Pick the appropriate rainwater pump and controller that meets the needs of the occupants

Rainwater tank requirements

In order to meet the set requirements, the installation of a water tank must be accepted by a building certifier during the construction approval process. All rainwater tank pipes work will require plumbing approval from a local council. Rainwater tanks are required to be attached to any swimming pool or spa (other than a spa in a bathroom) on the lot. The tank must also be attached to the required pedestals and washing machine cold water heaters, any external taps, and other fixtures as specified by the local government in a planning tool.

A rainwater tank must:

  • Possess a minimum storage volume to service a swimming pool in the whole lot. This volume will be contingent on the pool space (m2).
  • Possess a minimal storage of 1500 litres per mandatory pedestal
  • be attached to every required pedestal
  • be connected to washing machine cold water taps
  • be connected to an outside use.

Wet and dry systems

There are two sorts of systems used to direct the water from the roof catchment area into a rainwater tank. These are dry systems and wet systems. A sterile system comprises free-draining pipes that dry out and do not hold water after every rainfall event. A wet system consists of pipes which aren’t free-draining and water stays in the pipe function between storms. Wet systems can help in maximizing the usable roof catchment area. If a wet system is used, downpipes must be fitted using mosquito proof screens to prevent mosquitoes from entering the pipes and the machine. A way of draining a moist system should be integrated into the layout to avoid stagnation in the event of prolonged dry periods. Dry systems are usually recommended as any danger of mosquito breeding and water stagnation from the pipes is removed. It is also generally easier to maintain which means that relining the pipe would be a simpler process as compared to the wet system.

Leaf diversion

A screened downpipe rain head must be set up on each downpipe connected to the tank. The screen mesh should have openings no smaller than 4 mm and no larger than 6 mm and shall be designed to prevent leaves from entering the downpipe.

First flush apparatus

Roofed areas can protect water from contaminants such as bird droppings, dust and organic matter which may cause blocked drain or plumbing in your establishment. There is no mandatory requirement for a first flush device to be set up in which the minimal connections (toilet cisterns, washing machine cold water taps and an outside usage) are provided with water from a rainwater tank. To assist in preserving rainwater quality at which the rainwater tank is supplied to any additional connections (including showers, wash basins, kitchen or hot water services) a minimal 20 litres of the first flush out of the total roof catchment area, needs to be diverted /discarded before going into the rainwater tank. Individual site investigation is expected in heavy pollutant regions to determine if larger volumes of initial flush rainwater should be redirected. Rainwater from the very first flush system has to be discharged to the property’s overflow drainage system. Councils may decide to support first flush devices via a planning instrument.


Pumps have to be installed or positioned to guarantee sound levels do not create annoyance for neighbouring properties. Any rainwater tank pump system should be made to ensure maximum static pressure in any outlet or fixture does not exceed 500 kPa (kilopascals) and minimum pressure in the most disadvantaged socket or fixture isn’t less than 50 kPa (kilopascals) in the minimum flow rate required.


Green-coloured identification cassette marked “CAUTION RAINWATER LINE BURIED BELOW” should be utilized to identify:

  • Underground stormwater pipes into the tank
  • underground water supply pipes from the tank.


Rainwater tanks fitted with leaf-guards will generally keep out insects, plant and small creatures, though some maintenance is required to ensure effective on-going operation, water quality and health protection. Extensive management advice for rainwater tank methods is found in the monograph ‘Advice on the Use of Rainwater Tanks’. It includes advice on potential dangers, preventative measures, monitoring and maintenance.

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