Australian researchers have found large reserves of freshwater beneath oceans.

Water scarcity is growing by the day. Previously, other researchers had estimated that rising global temperatures would leave 500 million or more people without access to drinking water. The new research shows that humans might benefit from half a million cubic kilometres of (120,000 cubic miles) water from seabed on continental shelves.

The freshwater reserves have been found off the coast of Australia, China, North America and South Africa, researchers said.

Previously, researchers knew that freshwater reserves existed below the seabed, but believed that it was a rare phenomenon.

"The volume of this water resource is a hundred times greater than the amount we've extracted from the Earth's sub-surface in the past century since 1900," said lead author Dr Vincent Post of the Flinders University. "Knowing about these reserves is great news because this volume of water could sustain some regions for decades."

Dr Post said that it has taken hundreds of thousands of years for these water bodies to form. The sea level was much lower thousands of years ago than it is today. These reserves are protected by clay and sediments that accumulate above them.

 "So when it rained, the water would infiltrate into the ground and fill up the water table in areas that are nowadays under the sea," Dr Post "It happened all around the world, and when the sea level rose when ice caps started melting some 20,000 years ago, these areas were covered by the ocean.

Increase in food production and meat processing has led to a rise in water-use around the world. By 2030, 47 percent of people will be in regions with high water stress, AFP reported.

"Freshwater under the seabed is much less salty than seawater," Dr Post said in a news release. "This means it can be converted to drinking water with less energy than seawater desalination, and it would also leave us with a lot less hyper-saline water.

The study is published in the journal Nature.