Installing a rainwater tank underground can save space in your yard but costs around twice as much as above ground options. They need to be made from stronger materials and structures and often require weighting or concrete reinforcement. Because underground tanks are lower than the ground level you will need a pump. NSW regulations require additional backflow prevention due to the risk of groundwater contaminates.

The traditional round tank and some of the following space efficient options are the most popular.
Under the house: For houses on stumps or stilts a space saving option is to put the tank under the house or beneath decking. There are rainwater bladders available which are durable and can be installed with ease.
Against the wall: Another space saving option is tanks that go against walls or even act as garden walls. Some models can be joined together to make up larger water storages.