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Rainwater tanks range from 200-litre rain barrels (a simple barrel with a tap) to 25,000-litre tanks that connect to internal plumbing.

Choosing a rainwater tank size

When deciding what size rainwater tank is right for you, there are several things to consider:

• What will you use the water for (e.g. all outdoor use, some laundry use and toilet flushing, or drinking water and household use)?
• How much water are you likely to collect?
• How much space do you have for the rainwater tank?
• Will your rainwater tank be underground, above ground, or on the roof?
• What zone is your property in?

A registered plumber or rainwater tank supplier can have good advice on what rainwater tank to choose and the best location for it.

Retention tanks

Retention tanks store water for future use.

Water type	Water use	Tank type
Non-drinking water (non-potable)	Outdoor use (e.g. car washing, garden watering)	Non-potable retention tank or rain barrel
	Outdoor use (e.g. toilet flushing and laundry)	Non-potable retention tank
Drinking water, full drinking water supply (potable water)	Outdoor and indoor uses (e.g. kitchen and bathroom supply). Water must be purified.	Potable water retention tank (complete supply)
	Best suited to houses NOT connected to the centralised water network

Detention tanks

Detention tanks collect and store rainwater, then slowly release it back to the stormwater network.

This helps reduce the flow of stormwater runoff and minimises effects on the environment, like bank erosion, sewer and stormwater overflows.

A detention function can be added to a retention tank. This makes it a dual-purpose system.