How to Select a Water Tank

Selecting a water tank

Saving water for a rainy day (well, actually for a dry sunny day), is a clever idea. This is the first step in the rainwater harvesting process.

Rainwater harvesting makes sense and is an excellent way to use all those wasted litres of water running down the drain. Catching the rain makes even more sense when you ponder the fact that in Australia 50% of the annual average water consumption is used for flushing the toilet or watering garden. That amounts to a massive 250,000 to 300,000 litres per household of water literally going down the drain every year.

Using rainwater can potentially save millions of litres of water yearly and household money for other necessities.

Now when we have established that rainwater harvesting is a great idea, the next decision is what type of water tank is required to store the rainwater you collect.

The first step in the tank selection process is:  Decide how much water is needed, and is it for the household or the garden or for outdoor use?

How you want to use the water tank is a fundamental for selecting your water tank.

If your requirement is for outdoor water use only, such as for watering the garden or washing the car, then a simple calculation of daily watering use can be done. Household use can be restricted to the toilet and washing machine, which is a requirement in some council areas, or it can be used for the whole house. Depending on which part of the house uses the water, this will determine the annual usage.

The other factor to consider is how big is the household – does it comprise of just two people or is it a bigger family of 6. The best way to estimate your water usage need is to go to the water usage calculator on the Bushmans website Bushmans Tank Calculator

After the estimation of your water requirements, the next step is to work out how much water can be caught from the roof of the house, shed or other buildings where the rainfall is being harvested from. This a relatively simple calculation based on what the average annual rainfall in the local area is and how many square metres the roof the rain will be caught from. This calculation gives you the total litres that can be caught annually.

Once the total water catch is determined, then the next calculation is to work out how many times per year the tank can fill up. This calculation is based on the daily consumption and the rainfall patterns of the area. For example, if the area has a relatively even distribution of rain and is in a higher rainfall area, then it could be assumed the tank could fill 3 or 4 times a year. In drier areas, where the rain is falling in one season, then the tank may only fill twice a year. Bushmans website tank calculator page will help you make these calculations.

How big or small a tank do I need?

Now we know the amount of rainfall caught, and how much water is used, the next step is to work out how big your tank needs to be. This is done by calculating the amount of water caught by the number of times the tank will fill.

Note this process is not an exact science as annual rainfall can vary significantly as well as the annual consumption of water. The general recommendation is to always to go for a larger tank as it provides a buffer for drier years.

The other consideration is to select the shape and decide on what size tank you need. The shape of the tank needs to fit space available. Generally, it is a round or slimline design for above ground. Underground tanks also come in a range of shapes and sizes.

Your rain water tank supplier will install the tank for you. The tank installation is a great first step in the rain harvesting process and will immediately cut down your consumption of mains water.

Rain water tanks – different materials

Rainwater tanks are made in different materials which have a range of benefits and drawbacks.


Water tanks generally come in the following materials:

Polyethylene (plastic) or poly tanks are the most popular tank material as they are both cost effective and long lasting. Poly rainwater tanks are not subject to rusting and is therefore ideal for the harsh Australian climate, particularly in the areas around the ocean. The quality of the poly tank is important as this will ensure a long-lasting tank. Using raw materials such as Sunsmart® polyethylene will provide a better product.

  • Metal tanks are made from corrugated or flat rolled metal, which may be galvanised or coated. Some steel tanks use a material called Aquaplate® where as other use a poly liner. Which of these you select will depend on the size of the tank and personal choice. When you are looking for a larger tank such as 100,000 or 200,000 litres then a liner tank is what is required.
  • Fibreglass is a material which ensures that the tank is rust and chemical resistant. This option is quite expensive.
  • Tanks made from concrete are now mainly used for underground tanks and in some cases in fire areas. They have the benefits of not rusting, burning, melting or being blow away. They can be manufactured on site. They tend to be significantly more expensive thann poly and steel tanks.


You should contact and ask your local council and water supplier regarding specific rules and regulations in your area. Some councils require a submission of a development and building plan. Other rules that may apply include location of the tank, colour, size and noise issues if using a pump.

Are you renovating or building a new house?

If you are building a new home or renovating your house, there are legislative requirements in some states and council areas that may stipulate that energy and water efficient features such as a rainwater tank are included in your plan. Check with your local council.


When contacting your water tank supplier, ask what is included in the quote. (delivery, installation, extra materials such as a pump, pipes, fitting, taps, extra materials such as first-flush or backflow prevention and a stand.)

Preparing the Tank Installation Site

Before the tank is delivered it is important that the site and tank base has been prepared. The video below provides a good overview of what needs to be done.

Watch this video to find out the vital steps for selecting the right tank for your house, farm or commercial site

Author: H Lindholm