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Water tank sitting in a back garden surrounded but plants.


Catching rainwater and storing it in a tank is a great way to conserve water. With the right plumbing, the stored water can be used for things like watering the garden outside and flushing toilets inside the home. Check with your local building and water regulators before installing a tank to check local regulations, including the need for a building consent or permit.

Here are some things to take into consideration when choosing a water tank.

Safety tip: Always wear the appropriate safety equipment (safety glasses, gloves, ear muffs and a mask, for example) and always follow the instructions for the product or equipment.


1Determine the tank’s purpose

First, determine what you’ll be using the water tank for. Will you use it primarily outside, to water garden beds and the lawn? Or would you also like to use the water inside – to flush toilets, for example? Would you like to take the usage a step further and use the water to wash clothes or to bathe and shower? (It may be possible with the right system).

Once you’ve determined what you’ll be using your water tank for, you can start thinking about the size of the tank you’ll need, where you might want to place it, and how it will need to be plumbed.

Water tank in the back garden

2 Work out the size

The size of tank you’ll need is based on how much water you will use and how much you might collect in a season. Work with your plumber to calculate your usage as well as the amount of water you’re likely to collect.

Here’s a rough calculation to follow: Your roof area, from the roof that you will be collecting the water from (in square metres), multiplied by the annual average rainfall (in millimetres) in your area equals the maximum rain harvesting capacity (in litres). This will give you some idea of how much water you might be able to collect and store.

Bunnings team member touching the water tank

3 Choose the type of water tank

Once you know the capacity you’ll need, you can start looking at the various storage and placement options.

There are many different types and styles of rainwater tanks – for example, standard corrugated, slimline, below ground and even bladder tank systems that can be hidden under the deck. Each system has its pros and cons, so consider which elements are important to your needs.

Bunnings team member touching the water tank

4 Abide by regulations

There are always regulations to consider when adding things to your property and rainwater tanks are no exception.

The tank might have to be connected to a solenoid which helps bring water in from the mains if the tank runs dry, which can happen in hot, dry summers. Rainwater tanks must also be signed off by a registered plumber, who will ensure that everything is working safely and correctly. Check with your local building authority to see if you need a ‘building consent or permit’ – you may need one.

Bunnings team member reviewing the pipe connected to a water tank

5Looking for more inspiration?

For more sustainability and recycling inspiration, read our D.I.Y. section.

Health & Safety

Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions that came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings Team Member.

Grave health hazards are linked to asbestos, which may be in homes built up to 1990. Health hazards may result from exposure to lead-based paints in older materials and copper chromium arsenic (CCA) treated timber. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer. You can also use a simple test kit from Bunnings to indicate the presence of lead-based paint.