What Size Water Tank Do I Need?

by Oct 8, 2020Help & Advice

What sized water tank do I need? Good Question! The bigger the tank you more water you can store – obviously! However, when calculating the correct size for your requirements we also recommend you consider the following.

How Much Water Do You Need?


If you are intending to install a Whole House Water Filtration System with your Tank to provide all your water needs, then consider how much water you need each week.

While each circumstance is different a general rule is to plan for at least four weeks supply of water. For example, if you use 5000 litres per week then you should get a tank at least 20,000 litres in size. There are some approximate calculations you can do to get an idea of your water usage. For example, for a four-person family each person uses 120-200 litres each per day = 600 litres per day.

Another way to approach this is to consider – for a 22,800 litre tank: It will provide for approximately 4600 toilet flushes or 350 showers or 380 wash cycles or 23 hours of tap water.

How Much Space Do You Have Available?


Depending on the space available, you might need to decide whether to order a round or slimline tank(s). Round tanks are ideal where you have plenty of space and where you want a large volume of water.

Slimline Water Tanks are ideal for where you have limited space like under eaves for example. However slimline tanks don’t tend to store as much water as round tanks.

The round water tanks range in diameter from 900mm to 3900mm and in height from 300mm to 3100mm while the slimline tanks range from 1000mm to 4800mm in length, 550mm to 1180 mm in width and 300mm to 2350mm in height.

The maximum water storage for slimline tanks is 10,000 litres whereas for round tanks is 37,000 litres. If you work out that you need more litres, then you could consider linking up maybe three tanks side by side to triple the water storage capacity.

For linking dimensions in mms and water storage in litres visit Steel Water Tank Pricing

Should you go for one big tank or several smaller ones linked together?

It is easier to transport and place smaller tanks. We can place them in different locations so we can capture rainwater from different aspects or sides of a roof of roofs. One large tank takes less space but it could mean that you can only capture the water from one roof location.

From experience we have found that having three round tanks holding 30,000 litres each (total 90,000 litres) will easily keep that family in water all year round.


&How Much Water Can You Harvest From Your Roof?


As a general rule, each square metre of roof space collects around 1 litre of water for every one millimetre of rainfall.
So if we had:

10 millimetres of rain in a storm, and 150 square metres of roof space actually available to collect rain water

We could collect 1500 litres of rain water in that storm (150sq metres x10 millimetres x 1 litre)

To add to this calculation, you can look up the monthly rainfall pattern for your geographical area, maybe say 100mm per month on average over a 12-month period.

Consider your Location

When considering what size water tank do I need? Location is a big factor. The real value of your water tank comes in the driest months where water restrictions can be imposed. If you are living in an area which tends to have lower rainfall or where there is an extended dry period, then it is imperative to get the largest tank(s) to suit your needs and finances. For example, in SE Queensland the rainy season tends to be from December through to April but there is also an extended dry period from May through to October. If we are living in more inland areas then these dry periods can be even more problematic in terms of access to stored water unless we are well prepared.

To find out more about monthly Weather patterns visit our Gold Coast, Brisbane, Sunshine Coast ,Toowoomba  and Byron Bay pages.


What kind of Budget Do You Have?


When considering the question ‘What size water tank do I need? Cost is an important factor. In general, round tanks are less expensive than similar size slimline tanks because slimline tanks need internal reinforcing rods to keep the sides stable when they are full of water. This make them slightly more extensive but then they have the advantage that they can be fitted into narrow spaces.

Stainless steel tanks are slightly more expensive than tanks made from Colorbond but then stainless steel tanks have a longer 30-year warranty compared to the 20-year warranty for tanks made from Aquaplate/Colorbond. There are other differences. For example, Colorbond water tanks come in different colours while Stainless steel tanks are better in marine environments. Both tanks maintain structural integrity during bush fires and can be made bushfire compliant.


We hope we have provide some insights to the question ‘What size water tank do I need?‘  if you need any more help and advice please do reach out to us.

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