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. Due to the fact that a considerable amount 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.

Using rainwater in the garden

Rainwater can be applied from the tank to the garden by any of the following methods:

• Gravity-fed hose irrigation
• With a watering can – most useful to water pots and containers
• 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

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.

For example, 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.

Roof area (m2) = roof length x width

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

Below is a guide to how far particular sized tanks will go when full.

1700 L rainwater tank

• 120 metres of Gravity-fed dripline (8 litre per hour drippers) for 30 minutes
• Hand-held garden hose
• Pumped sprinkler system for 50 minutes

2250 L rainwater tank

• 190 metres of Gravity-fed dripline (8 litre per hour drippers) for 30 minutes
• Hand-held garden hose
• Pumped sprinkler system for 65 minutes

4500 L rainwater tank

• 350 metres of Gravity-fed dripline for (8 litre per hour drippers) for 30 minutes
• Hand-held garden hose
• Pumped sprinkler system for 130 minutes

For tanks that carry 10,000 litres or more we recommend that you seek the assistance of a qualified staff member or professional consultant to tailor a system to suit your water needs.

Lawn sprinklers can use at least 800 – 1200 litres of water in a week. It is not practical to use tank water to irrigate a lawn unless you have a large tank. Also lawns usually require watering during the driest part of the year when the tank is least likely to be full.

Other Considerations

• Check with your local water authority on watering restrictions as sprinklers may not be used in some areas of Australia. Click here for a list of Australian Water Links.
• Suitable site: aesthetic, space required, and access to supply from stormwater and overflow drainage point
• Potential for gravity feed or the need for a pump
• Installation requirements
• Stable base

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.

Installation

Please note that many rainwater systems require a licenced plumber to install them.

Rebates

Many Australian Water Authorities have introduced a rebate system for rainwater tanks, greywater systems, irrigation systems and mulches. Click here for a list of Australian Water Links.