Large amounts of water can be found beneath the Earth’s surface.
As water shortages become increasingly problematic in many parts of the world, scientists have been delving deep underground to find out just how much there is locked away in the rocks.
According to the latest report there is a staggering 5.42 cubic miles of water trapped beneath the ground, but only around 6% of it is regularly cycled through the hydrological system.
The rest, which is located deep underground and takes millions of years to replenish, is far too salty – more so than even the oceans – and can also contain toxic elements such as arsenic and uranium.
“We’re using our groundwater resources too fast – faster than they’re being renewed,” said Dr Tom Gleeson, a hydrogeologist at the University of Victoria. “Since we now know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out.”
The geographic distribution of modern groundwater is such that most of it can be found in tropical and mountainous regions while the older, deeper reserves are more prominent in arid regions.