Deep beneath the Earth’s surface from New York to West Virginia sits the Marcellus Shale, an enormous geological deposit of natural gas. Natural gas is one of the cleanest fuels available  if you can extract it without ruining the water around it.

Retrieving Marcellus natural gas requires hydraulic fracturing with horizontal drilling, a process that shoots millions of gallons of water deep underground to break the rock and unlock the gas. Now that prospectors are using this process increasingly in Pennsylvania and hoping to begin soon in New York, there are two important questions: Where will all that water come from? And what happens to it when it is no longer needed?

New York officials are exploring whether it’s possible to drill safely without poisoning water supplies. High on our list of concerns is whether the used water  some of it tainted with toxic chemicals  will later seep into streams, rivers and deep water wells, placing New York City’s municipal water supply at risk. Before the state allows exploration, there should be a clear agreement on how the used water will be dealt with safely.

Energy companies have already signed so many new leases for drilling rights with landowners in New York and Pennsylvania that one farmer called it a “modern-day gold rush.” Nobody wants to deprive these landowners of the money they can make, but the price of their good fortune cannot be the contamination of water supplies for everyone else.