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What size water tank do I need for a family of 4?
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What size water tank do I need for a family of 4?

Apr 27, 2021

When it comes to selecting a water tank for your home, the important question is, how big do you need to go? There’d be nothing worse than going through the process of buying and installing a water tank, only to find that you are always that little bit short when the fourth person goes to have their shower at the end of the night!

It is paramount when selecting your tank that you get the specifications right. But the question is, how much water does the average person need? If we figure that out, we can identify how big a

How many Litres of water does a family of 4 use per day?

First of all, how much does the average Australian household consume? Certainly, water usage varies greatly across the country, but on average, the regular Australian household goes through between 165 and 340 litres of water per person, per day.

So, a family of 4 in Australia, uses up to 1360 litres of water per day.

In the drier, inland areas, the average amount per person goes up to around 800 litres!


What do we use our water for?

Whilst we use a lot of water, what is important is where that water consumption is going. A study carried out by the Australian government found that 35% of our water usage is for irrigating our gardens, whereas 19% of it is flushed down the toilet.

The numbers show that an average toilet uses 12 litres of water per flush. Whereas a typical garden irrigation system uses 1,000 litres of water per hour!

Although most people do not need to water their plants every day, the cumulative impact that it has over time is tremendous.

  • 50% – Outdoor use (car washing, hosing driveways, garden use)
  • 17% – Showers
  • 13% – Toilets
  • 11.5% – Laundry
  • 8.5% – Other (includes drinking)

The process of treating water in order to make it usable for households is costly and time consuming. That, and it involves an incredibly complicated filtration and chemical treatment process, then pumping the water all of the way to your home.

As with all major industrial operations, wastewater treatments produce a lot of greenhouse gases, thus having a negative impact on our environment.

You can always switch to rainwater

We need safe and clean water in order to maintain our health (i.e., for bathing and drinking). Having a properly established rainwater tank system is ideal for such activities. But aside from consumption, rain water is ideal for flushing toilets and irrigating our gardens.

By switching to a rainwater tank, you can save up to 35% of the water that you consume!

What size water heater do I need for a 4 bedroom 3 bath house?

For water heaters, what size do you need? Here are some easy figures for you:

  • 1-2 people: 30-gallon water heater
  • 2-3 people: 40-gallon water heater
  • 3-4 people: 40-50-gallon water heater
  • 5 or more people: 50-80-gallon water heater

So, for an average 4-person house, you should be looking at around 50 gallons!

How big should my water tank be?

The size of your water tank should be large enough to accommodate your family. When investing in a water tank, you should also be mindful of the fact that it isn’t something that you should need to replace in a hurry.

The fact that some fibreglass water tanks can last up to 50 years, means that if you plan it right, you should never need to replace it in your lifetime. This means that you need to accommodate for any changes in your family size.

For example, if you don’t have any children yet but plan to start a family, then you need to account for that fact when selecting the size of your water tank.

The same applies if you have the one child, but are thinking of extending your family and having another one or two children.

As they grow older, their water consumption will grow significantly as well. Particularly when you get to those teenage years where you can’t seem to get them out of the shower!

Of course, it isn’t the end of the world if you don’t plan thoroughly and end up having children by mistakes. They aren’t always planned, but fortunately, you can simply double up and add another water tank to the mix if and when you need to.

In any case, it’s better to be prepared just in case.

Calculating the right size water tank for you will all depend on the rainwater capacity that you need.

For a 3-bedroom house, you’ll need around 15,000 litres of water storage (which is approximately a month’s worth). This is based on the assumption that you each use around 165 litres of water per day.

Then again, it all depends on what you are using the water for. For example, if you only plan to use your rain water for outside activities (i.e., watering your garden, washing your car etc.), then you can drop your water storage to about 7,500 litres.

Don’t worry, we understand how confusing it can get trying to figure this all out. If you aren’t much of a numbers person and you want to be safe, then you can ask a reputable supplier such as Safe Fiberglass Tank to help you.

They will be able to help you easily calculate how much water storage you will need, and then set you up with an awesome fibreglass tank that will last you a lifetime!


In conclusion, for a family of 4, you’re going to need a pretty big water tank! Perhaps something around the 8-9,000-gallon mark should do the trick. But again, it all depends on what you plan to use the water for, and how active your family is. Speak to the professionals if you are unsure, before moving ahead and paying for anything.