Scientists have discovered a massive reserve of freshwater trapped beneath the seabed that could provide water to the world's coastal cities and mitigate the impact of a looming global water crisis, according to a new study.

The study first reported in the journal Nature describes an estimated half-a-million cubic kilometers of low-salinity water buried in undersea aquifers off the coasts of Australia, China, North America and South Africa.

"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," the study's lead author Dr. Vincent Post said, according to Science Daily. "Knowing about these reserves is great news because this volume of water could sustain some regions for decades."

The undersea reserves have the potential to alleviate the impacts of freshwater scarcity on the planet, Post said, but the resource should be treated with care. Offshore oil and gas exploration or carbon sequestration activities could contaminate the aquifers, which are themselves a limited resource.

"We should use them carefully," Post said "Once gone, they won't be replenished until the sea level drops again, which is not likely to happen for a very long time."

READ MORE: Immense Freshwater Reserves Discovered Beneath Ocean Floor