Subterranean caves in the Blue Mountains have been
converted into observatories to quantify how water moves through buried rock structures into groundwater.
Groundwater forms the world’s largest active repository of fresh water—more than a hundred times larger than rivers and lakes combined.
To use that groundwater resource sustainably, we need to know that we are only using as much water as is being continually replaced, mostly via rainfall and underground leakage from rivers.