“You would have learned about the “water cycle” in primary school – water’s journey, from evaporation to rainfall to flowing in a stream or sinking into the ground to become groundwater.

Despite how simple it sounds, there are actually some large unknowns in the cycle – especially concerning groundwater.

We don’t know, for example, how fast aquifers – porous rock layers saturated with water – recharge. Or how much water actually makes it underground. And how much rain do you need to refill these underground reservoirs?

These questions are crucial because we rely very heavily on groundwater. It’s far and away the world’s largest source of fresh water we can access. There’s more water in the polar ice, but we can’t use it.

Our research team has been exploring a new approach to groundwater: going down to where the water is, using caves, tunnels and mines. We have installed a new network of groundwater sensors in 14 sites across Australia’s southeast – some more than 100 metres below the surface.

This is already giving us valuable data. For instance, in old mines in the Victorian gold mining town of Walhalla, we found it took more rain than we expected to start the recharge.”