A rainwater conservation system involves collecting rainwater from the roof and storing it in a tank for later use as irrigation water. Recycling rainwater for use on garden beds is an excellent way of reducing household water that must otherwise be purchased from water companies. Considering that around 30% of household water goes on the garden, this is a great way of saving money whilst conserving the amount of water in our storage dams.

It used to be that only farmers had rainwater tanks. But now things have changed and the popularity of the humble rainwater tank has skyrocketed in recent years, following the introduction of water restrictions across the country. Perhaps the boom has peaked in some parts but as the threat of stage 4 restrictions loom for Melbourne, tanks look set to play a massive role in our gardens for a long while yet. So where do we start with tanks? There is so much info to digest. What type of tank should I get? How much water will I need? What pump is best for my situation? So lets start with the basics and talk about the pros and cons of installing a water tank.


Rainwater can help to make you more self-sufficient. It provides a back-up supply in case of further water restrictions, water shortages, or water quality problems. Rainwater can be cleaner than mains, bore or dam water because it lacks many of the nasty chemicals. However we advise against drinking urban tank water, particularly when the mains supply is so good. Using tank water can definitely save you big money on your water bills. In fact you can reduce reticulated water use by 50 to 100 percent in urban areas. This is great for the environment because it helps to reduce the energy used for pumping water as well as infrastructure operating costs. It also lessens the need for new dam construction and protects remaining environmental flows in rivers.


Tanks are a fairly expensive item to buy especially when you take into consideration the preparation work and installation. However, think of a tank as a long-term investment that could see you save money in the long run. They also need regular maintenance. It is a good idea to regularly check and clean the gutters to prevent leaf litter build up. This will save you problems in the future.

Using rainwater in the garden

Rainwater can be applied from the tank to the garden by Gravity-fed hose irrigation, with a watering can – most useful to water pots and containers or it can be pumped from the tank to irrigation systems within the garden.

Will a system work at my house?
The type of rainwater system you choose will be determined by your water use requirements, the space you have available for a tank, the collection area of your roof, and the cost of each system. For a small or inner city garden where tank size is limited, a tank connected to a gravity-fed hose and supply for hand watering is most appropriate. The minimum tank size recommend for use with a pump-fed irrigation system is 2000 litres. Mains water can be linked into the system and accessed by an automated switch-over mechanism, as a backup water source if tank water runs out.

Choosing a tank

The type of tank you should get depends on a number of factors, namely how much room you have, what the water will be used for and how much you’re willing to spend. Plastic tanks respond well to bumps, are non-corrosive, and are usually the cheapest to buy. You can also purchase underground tanks, bladders that fit under houses, and concrete tanks

Melbourne averages approximately 50 mm of rainfall each month, on an average rainy day (4.5 mm of rainfall) a roof of 150m2 will catch 675 litres of water. In order to collect all of this water, your tank will have to be at least this big. During the wetter months of the year, you may not use your tank at all, in this instance the same size roof has the potential to catch more than 7,500 litres over the month.

Tip: To calculate the water that a tank is able to capture off your roof multiply the length by the width of the roof and then multiply this figure by the amount of rainfall over a particular time.

Roof area (m2) = roof length x width

Water captured (litres) = roof area x rainfall over time period


There is no need to go overboard but ‘the bigger, the better’ when it comes to tanks. If your tank holds more water then you are likely to use less reticulated water. As a good rule, your tank should at least hold a 4 week supply of water. If you live in an area where rainfall is frequent then you can get by with a smaller tank. On the flip side, if it doesn’t rain much in your area then a bigger tank is the way to go. If the water is to be used for the garden you should have a minimum of at least 2000 litres. Any smaller than that and it isn’t really worth the effort. The range of tanks available is ever increasing, systems are available that can go underneath the house or decking, under the ground, become a wall or are ornamental in their own right. If you have looked at installing a tank in the past but found that nothing was suitable, you may find that today’s range might include something that is perfect for you.

Base Preparation

It is very important that the area where the tank is going to be located is level. In most cases it is advisable to lay sand, crushed rock or concrete down as a base. Depending on the company, some tank warranties may be voided if the tank base does not match the those outlined in the installation instructions. So make sure you check the instructions before you install the tank.


The final stage of actually installing the tank should be carried out by a licensed plumber. You may know what you’re doing, but some warranties may be void if the tank is not installed by a registered plumber, and proof of certification is needed when you apply for the government rebates. Plumbing regulations state that drainage and water supply work must be carried out by a licensed plumber. This includes plumbing overflow back into the stormwater system.