May 30

What size rainwater tank do I need?

Share this

What size rainwater tank do I need?

colorbond rainwater tank built next to home in australia

More than three million Australian homes have some form of rainwater tank installed; over half a million of those homes rely on rainwater as the primary water source for their family, while the other 2.5 million use their rainwater tank for drinking water, gardening and reticulation, laundry, and other minor uses.

This means that everyone needs a different size rainwater tank, as there are a range of factors involved including roof size, annual rainfall, household size and water usage, and that's after taking into consideration what the tank will be used for.

For people without much space on their property, there are a range of slimline or flat design poly water tanks available to fit in smaller spaces. Where space isn't a factor, large steel water tanks provide the best value the larger these water tanks get.

As a rule, once you need to purchase more than one slimline or plastic tank to meet your storage requirements,
steel water tanks become the cheaper option.

There are a range of benefits and reasons people use rainwater tanks for, including:

  • Reduction or removal of a water bill
  • Fresher tasting drinking water
  • Access to water for gardens year-round
  • No reliance on council or scheme water
  • Fire protection
  • Water for washing machine and laundry
  • Ability to move off-grid
  • Reducing stormwater runoff

Pioneer Water Tanks manufacture rainwater tanks for rural and semi-rural customers with water tank sizes from 12,000 litres to 500,000 litres, so for the purposes of this post, we will be looking at rainwater tanks for the collection and storage of rainwater for the entire home.

How much water am I going to need to store?

The average Australian uses around 120,000L of water a year, but this figure is skewed by high water users, and not geared toward the average family who typically uses significantly less water than this.

Pioneer Water Tanks recommends a starting size of 60,000 litres of storage for one person, plus an additional 30,000 litres for any additional people who are living in the home.

These figures are averages based on our experience, and additional storage may be required for families with animals and pets, large gardens or older appliances that use more water than modern water-saving designs.

Pioneer customer Jamie Adamson is a great example of this when his family installed a 60,000 litre rainwater tank on their property in Taggerty which they thought was going to be sufficient.

However, when they did some landscaping on their gardens, they found that they didn't have enough
water for their home and garden through the summer months.

Eventually, the Adamsons got back in touch with Pioneer and installed a second GT60, increasing their total water storage capacity to 120,000 litres, and meeting their water storage requirements.

“These are big capital items and you’re not looking to replace them anytime soon – it (the warranty) gives you a lot of comfort knowing you’re covered,"

Jamie Adamson - Taggerty, VIC

two 60,000 litre rainwater tanks next to an off-grid home in victoria

How much rainwater can I harvest?

Just as important as how much water supply you need when determining the best rainwater tank size for your property is how much rainwater you are able to harvest, as a tank much larger than this will likely never get full - unless you are using it as a holiday home.

The equation to determine this is an easy one; simply multiply your annual rainfall in millimetres by your roof size in meters squared and you will have your annual rainwater harvesting ability in litres. Alternatively you can use our rainwater harvesting calculator.


Calculate Your Year’s Supply Of Water

To work out how much rainwater you can harvest from your roof (catchment area) use the simple calculator below:

For example, a family at Margaret River living in a home with a 200m² roof area would be able to harvest 193,000 litres of rainfall annually (rainfall of 965mm a year taken from Bureau of Meteorology Witchcliffe site).

It is important to remember this number doesn't represent how large you need your rainwater tank to be - as you will be using this water throughout the year and it won't all fall at once - rather the amount you can harvest total.

If you have a shed, patio, garage or gazebo on your property, you can also utilise the roofs of these structures as catchment area for additional rainwater collection.

a large zincalume water tank built next to a large steel shed in western australia

In the best case scenario, you may realise you can harvest more rainwater than you need.

When Natalie and Andrew made the switch to off-grid living, no longer wanting to rely on mains water, they installed a GT200 water tank with 200,000 litres of water storage for their home and garden.

However, four years later they realised that while they had opted for a large enough water tank size for their home, they were experiencing a significant amount of overflow which Natalie felt was a waste.

So they decided to return to
Pioneer dealer Huckleberry Tanks, and purchase a second GT200, increasing their capacity and giving them a significant bushfire reserve, and the freedom to use their water as they please.

“We wanted to purchase another tank and connect it to the existing one to catch that over-flow. It’s also a lot cheaper than a dam, and you don’t have evaporation,"

Natalie - Paynedale, WA

a woman and two dogs standing between two large colorbond rainwater tanks

What can I do if I can't harvest enough rainfall?

While you are always going to be limited by your rain-harvesting areas and the annual rainfall of your property, there is one way you can increase the volume of water you can capture.

Capture the water straight from your tank roof.

Smart Water Savers are an innovative water tank accessory designed by a member of the Pioneer family, allowing you to utilise your tank roof as a catchment area without the pitfalls of tank gutter systems

The amount of water you can harvest will depend on the size tank you have installed, but it can come in handy if you do find yourself falling short.

Our most common model - the GT110 - can increase your total rainwater harvesting area by 50m², which would give you another 15,000 to 20,000 litres of stored water even in parts of Australia where the climate only sees a few months of wet weather a year.

Pioneer Water Tanks offers these Smart Water Savers, as well as a range of standard and non-standard
fittings and accessories across the whole range of residential rainwater storage products.

When Spence and Kerrie turned to Pioneer Water Tanks for
their move off-grid in regional Victoria, they opted for the Smart Water Savers to ensure their 250,000 litre water tank didn't run out of water in the summer.

“That technology was so simple and so clever, and it works out that we get an extra 35,000L a year just off the roof of the water tank. There’s a lot of water tank providers out there that don’t have that facility,”

Spence Thompson - Mia Mia, VIC

Kerrie and Spence from The Block (2018) in front of their Pioneer Water Tank

Rainwater tanks for bushfire protection

For some parts of Australia there is a minimum requirement of water storage for bushfire protection to be used by emergency services in the event of a fire.

You can do this by installing a separate water tank on your property, or if you think two tanks in one location would take up too much space, Pioneer Water Tanks has made that decision easier for you.

Instead of installing a second tank, you can have a fire reserve and household water all in one system. This is done by placing the main outlet slightly higher up on the tank, and the fire outlet at the base so that there is always water in the tank for fire.

Pioneer Water Tanks have been tested in fire conditions, and are the best choice for bushfire protection. You can read the
articles by the Bushfire CRC here.

How to calculate rainwater tank size:

If you have just purchased a property with a rainwater tank installed on it, you may be wondering what size this water tank is and how to determine water tank size.

For Pioneer Water Tanks it is relatively simple to do calculations without a tape measure. If you count the number of bolt strip covers round the outside of the tank and then give us a call, we will be able to determine the water tank size for you.

A 110,000-litre water tank has 12 of these bolt strips around the outside.

However, if you have a tape measure handy, or are trying to calculate the volume of a non-Pioneer Water Tank, you're going to need a calculator.

Tape Measure

The equation for how to calculate the size of a water tank is: 

π x radius² (m) x height (m) = volume (kL) 

So, for a tank with a diameter of 8.02m that is 2.18m tall, the calculation would be;


3.14 (π) x [4.01 x 4.01] (r²) x 2.18 (h) = 110kL

water tank installed in welshpool WA

Want information about rainwater tanks for your home?

Pioneer Water Tanks have been manufacturing, supplying and installing rainwater tanks all across Australia for more than 30 years, and continue to lead the way in water across the country and around the world.

If you have any questions about your next rainwater tank idea, or would like a quote or estimate from one of our expert dealers and installers, get in touch with us today.

Our team of experienced water tank sales staff and installation experts can offer you helpful advice on your water storage, whatever the demand of your home or property.

For more information or pricing on world-class water storage today, call 1800 999 599 or fill out our form online, and we'll be in touch shortly.

Loved this? Spread the word