Maximum depth - 3000 m
Area - 1,711,000 square kilometres
Total stored water - 8,700 million megalitres
Age of water - about 2 million years
Water temperature - average 30-50°, max 100°C

The Great Artesian Basin is one of the largest artesian (underground water) groundwater basins in the world. It lies underneath approximately one-fifth of Australia and extends beneath desert and semi-desert regions of Queensland, New South Wales, South Australia and the Northern Territory, stretching from the Great Dividing Range to the Lake Eyre. The Basin covers a total area of over 1,711,000 square km and it has an estimated total water storage of 8,700 million megalitres (a megalitre is one million litres and is equivalent
to about half the water in an Olympic swimming pool).

The Great Artesian Basin was formed between 100 and 250 million years ago and consists of layers of sandstone aquifers and water resistant siltstones and mudstones. The thickness of this sequence varies from less than 100 metres on the Basin edges to over 3,000 metres in the deeper parts of the Basin. Water holes called bores vary in depth from up to 2 000 metres with the average being 500 metres. Some of the sandstone contain oil and gas where conditions are suitable.

Groundwater in the Basin flows generally westward to the south-west over most of the Basin but to the north-west and north in the northern section. The rate at which water flows through the sandstones varies between one and five metres per year. Sometimes rain water refills into some exposed sandstone aquifers, mainly along the eastern edges of the Basin, more specifically along the western slopes of the Great Dividing Range. Natural water loss occurs mainly from small hills that release water (mound springs) in the south-western area. Mound springs are natural outlets of the artesian aquifers from which groundwater flows to the surface. Dating of the artesian waters has given ages of almost 2 million years for the oldest waters, which occur in the south-western area of the Basin. Water quality in the main aquifers is generally good although it is very acidic and high salt levels make it generally unsuitable as farm water. Water temperatures vary from 30 degrees C in the shallower areas to over 100 degrees C in the deeper areas.