CSG has the potential to change the functioning of aquifers, the director of the National Centre for Groundwater Research and Training (NGCRT) said, but as yet no conclusions can be drawn.

There are some areas to watch, however.

"We know that in order to release gas from methane beds we need to depressurise these beds to extract the gas from the coal," Prof. Simmons said.

"We know that CSG can lead to depressurisation of aquifers, which leads to questions about water availability.

"There are questions about the connectivity between aquifers that are being depressurised, and these are connected to surface waters - lakes, wetlands and rivers.

CSG also needs to dispose of big volumes of water brought up with the gas.

"It's not fresh water, it's saline or at least brackish, so there is a huge question mark about how much water is coming up that needs disposal, whether we're going to desalinate that water, or dispose of it in salt disposal basins or put it in underground repositories."

And some key questions about the hydrogeology of methane beds remain to be answered.

"We don't know how much recharge is going on, the connections between aquifers, the properties of the rock - there are questions that need to be tightened up in assessments of CSG."

On the positive side, Prof. Simmons thinks that CSG will need to operate within a tailor-made groundwater policy framework, and that will focus some much-needed attention on groundwater management in general.