The future cleanliness of the Washington region’s drinking water has unexpectedly become a central concern in the national debate over the controversial natural-gas drilling method known as “fracking.”

The gas industry is pushing to allow fracking in the George Washington National Forest, despite fears that it could threaten the cleanliness of the Potomac River. It’s the sole source of drinking water for more than 4 million people in our area.

It’s no surprise that environmental groups are pushing hard to ban fracking in the forest, which includes the Potomac’s headwaters in the Appalachian Mountains.

But I’ve been struck by the strong positions taken by more neutral parties, notably major local water utilities. The D.C. Water and Sewer Authority, the Washington Aqueduct and the Fairfax County Water Authority all oppose fracking in the forest — at least until the dangers are better understood.

“If we permitted it and we were wrong, it would be a catastrophic problem for the nation’s capital,” D.C. Water General Manager George Hawkins said.

“When you consider the risks to a headwater stream in a pristine national forest . . . this is a case where you would err on the side of caution,” he said.

Numerous cities and counties in western Virginia near the forest also are supporting a ban.

A decision by the federal government is expected in the next few months. The sensible thing is to wait two or three years, when we’ll know more about the risks.

The Environmental Protection Agency is doing a major scientific study of whether fracking (the common term for horizontal drilling and hydraulic fracturing) contaminates water supplies.

The report should be complete by 2016 or 2017. It will be the most thorough, authoritative examination of the issue.

We don’t need the gas right away. There’s lots of fracking yet to be done in spots in Pennsylvania, West Virginia and elsewhere that don’t sit in the highlands of a heavily populated watershed.

Both sides make persuasive arguments about the rewards or risks of fracking. It involves injecting millions of gallons of water, sand and chemicals into the earth under high pressure to fracture shale rock and release gas.

The gas industry argues that it has used the technique safely for decades. It stresses that the surge in fracking in recent years has dramatically increased U.S. natural gas production. That’s a plus, because we rely less on the Middle East for energy and because natural gas is cleaner to burn than coal.

Citing those advantages, Hawkins says D.C. Water is “not ideologically opposed to fracking.”

But critics worry that toxic chemicals could leak or spill during the mining or in the disposal afterward of vast amounts of waste fluids. They note that fracking is now taking place on a larger scale and closer to population centers than in the past.

It doesn’t help that the drilling companies won’t disclose all of the chemicals they shoot into the ground. They say that’s a commercial secret.

It also doesn’t help that fracking is exempted from meeting some standards of the Safe Drinking Water Act. That’s known as the “Halliburton loophole,” in honor of the giant oil field services company once headed by Dick Cheney. He was vice president in 2005 when the provision was adopted.

The George Washington forest case is critical mainly because of an accident of timing. The forest is about to adopt a new, 15-year management plan. So the decision could influence what happens in other national forests.

“Is this the beginning of, ‘Let’s just ban this on all federal lands’? I’m more concerned about that than anything else,” Greg Kozera, president of the Virginia Oil and Gas Association, said.

Technically, a U.S. Forest Service regional official in Atlanta will make the choice. The matter is so politically sensitive that either the Agriculture Department, which oversees the Forest Service, or the White House will decide.

The debate over fracking has been raging for years. Until now, however, it has not had such potential to affect the Washington region directly.

As a result, environmentalists have begun an effort to raise grass-roots awareness. A public meeting at the Arlington Central Library drew 50 people Monday.

“It’s our turn to consider the risks of fracking,” said Dusty Horwitt, a senior analyst at Earthworks, who helped organize the forum.

If the EPA and local water authorities conclude that we can drill for the forest’s natural gas without fouling our water or creating other serious problems, then go for it. But it’s only common sense to be sure beforehand.

For previous columns, go to washingtonpost.com/mccartney.