Sydney: An ancient underground water basin the size of Libya holds the key to Australia avoiding a water crisis as climate change bites the drought-hit nation.

Australia's Great Artesian Basin is one of the largest artesian groundwater basins in the world, covering 1.7 million sq kms (656,370 sq miles) and lying beneath one-fifth of Australia.

The basin holds 65 million gigaliters of water, about 820 times the amount of surface water in Australia, and enough to cover the Earth's land mass under half a meter of water, says the Great Artesian Basin Coordinating Committee.

And it is slowly topped up with 1 million megaliters a year as rain filters through porous sandstone rock, becoming trapped in the underground basin.

"There is probably enough water in there to last Australia's needs for 1,500 years, if we wanted to use it all," says John Hillier, a hydrogeologist who has just completed the Great Artesian Basin Resource Study.

But he and other experts warn that access to the basin's water supply is under threat from declining artesian pressure, which forces the water to the surface via bores and springs.

If artesian pressure falls too far, due to excessive extraction of water, the ancient water source will be unreachable, except through costly pumping.

Lying as much as two kms (1.2 miles) below ground, some parts of the basin are 3 km deep (1.8 miles) from top to bottom.

The basin was formed between 100 and 250 million years ago and consists of alternating layers of waterbearing sandstone aquifers and non-waterbearing siltstones and mudstones.

Basin water is extracted through bores and is the only source of water for mining, tourism and grazing in Queensland, New South Wales and South Australia states, and the Northern Territory.

The underground water spawns A$3.5 billion (US$2.4 billion) worth of production a year from farming, mining and tourism, says the Great Artesian Basin Coordinating Committee.

Source : Reuters