Artesian water is underground water confined and pressurised within a porous and permeable geological formation. Formations that store and transmit water are referred to as aquifers. When one of these aquifers is tapped by a bore, artesian water may flow naturally to the surface.
The Great Artesian Basin is one of the most important water resources in Australia. It underlies an area of 1.7 million square kilometres, approximately 22 per cent of the continent – including 12 percent of New South Wales.
The basin is the largest and deepest artesian basin in the world. The basin is 3,000 metres (9,800 ft) deep in places and is estimated to contain 64,900 cubic kilometres (15,600 cu mi) of groundwater.
It is the only source of reliable water for human activity and water-dependent ecosystems in much of the arid and semi-arid landscape overlaying the Basin in Queensland, New South Wales, South Australia and the Northern Territory.
The water of the Great Artesian Basin is held in several sandstone layers laid down by continental erosion of higher ground during the Triassic, Jurassic, and early Cretaceous periods.
During a time when much of what is now inland Australia was below sea level, the sandstone was then covered by a layer of marine sedimentary rock shortly afterwards, which formed a confining layer – thus trapping water in the sandstone aquifer.
The eastern edge of the basin was uplifted when the Great Dividing Range formed. The other side was created from the landforms of the Central Eastern Lowlands and the Great Western Plateau to the west.
The impermeable rocks confine the aquifers, causing the groundwater to become pressurised. In most areas the water is under sufficient pressure to provide a flowing source once it rises to the surface through artesian bores and natural springs.