PITTSBURGH — What causes clear, fresh country well water to turn orange or black, or smell so bad that it’s undrinkable?

Residents of a western Pennsylvania community have been trying for more than a year to get that question answered in their quest to get clean water back.

Some of them say the water was spoiled by drilling deep underground for natural gas. Others point to pollution from old coal mines. They’ve also been told it could even be a baffling mix of natural and manmade reasons that change the water over time, like the leaves change on trees. But no one knows for sure, and they say the uncertainty is maddening.

In late 2011, the drinking water for about a dozen residents in the Woodlands, a rural community about 30 miles north of Pittsburgh, began to change. At first, the families blamed gas drilling, or fracking, being done 2000 feet away. But state tests showed the water wasn’t contaminated by drilling, and even more confusingly, many of their neighbors reported no problems.

Families with bad water then turned to federal officials. But last summer the U.S. Environmental Protection Agency quietly sent a letter to one resident, Janet McIntyre, saying the agency agreed with the state finding, since most of the chemicals found in the water could have occurred naturally.

McIntyre wasn’t satisfied, noting that the EPA “never set foot on my property to test the water themselves.” The EPA didn’t respond to a request for comment on why the agency didn’t retest the water.

Still, the residents with water problems were hopeful that the Atlanta-based U.S. Agency for Toxic Substances and Disease Registry was looking at the issue. But last month the agency said it “is not actively investigating complaints from this area.”

“I’m just very, very frustrated,” McIntyre said.

So was John Stolz.

He’s the director of the Duquesne University Center for Environmental Research in Pittsburgh. Stolz said state and federal agencies failed to do detailed reviews, so a Duquesne team has been monitoring water quality and surveying households in the Woodlands, in what is one of the most in-depth surveys of alleged impacts of gas drilling in the nation. With funding from two foundations, a team has regularly tested area water for more than a year.

“We’ll see black water, we’ll see orange water, there’s often times an odor,” Stolz said.

Overall, about 50 out of the 150 households in the community have complaints. “There are certain areas that clearly don’t have any problems,” Stoltz said. And, he added, a well that has bad water one month may be clear the next, and a few homeowners even say that their well water improved after gas drilling began.

Even in areas with no nearby oil and gas drilling, the water quality in some aquifers changes naturally, groundwater experts say.

“It varies even within the same aquifer. It can vary from the top of the aquifer to the bottom, and from one side to the next,” said Mike Paque, executive director of the Oklahoma-based Ground Water Protection Council.

The wells themselves may be causing the problem, too. Stoltz said the depths vary from 90 feet to 900 feet deep, with an average of about 130 feet. Pennsylvania is one of the only states with no standards for rural water well construction, meaning multiple other factors could be contributing to the problems.

Others say the cause could be old coal mines or old oil and gas wells that date back to the 1800s.

Shafts from old mines lie under the region, said Butler County commissioner William L. McCarrier, who worked as a water well driller in the area during the 1970s. Those can fill with water, and that water then gets contaminated. He said pollution from old mines and wells was a common problem long before the recent gas drilling boom, which began about five years ago, adding that the situation is more complicated than many outsiders realize.

“It’s very unclear where the problem came from,” McCarrier said. He said he accepts the state finding that drilling didn’t cause the problem, but that authorities are still trying to find solution for the people who say their water is undrinkable.

That has put local officials in the middle of a fight.

The Woodlands is an unincorporated area that was laid out with no rights of way for public water or sewer lines, and even the idea of extending a public water line to the area has created divisions. Some people who live within a quarter mile of McIntyre say they have no water problems whatsoever, and they don’t want to pay for improvements they don’t see a need for.

McIntyre said a water company is willing to bring a feed line to the edge of the community and put a pump house in. But the Woodlands residents would still need to form an association to manage and pay for water lines and hookups.

Residents met in January with lawyers to discuss filing lawsuits. But one expert said any claim would be complicated by the variations in water quality and the lack of a contamination finding from state or federal agencies.

“It’s a tremendously difficult case,” said Emily A. Collins, a professor and supervising attorney with the University of Pittsburgh Environmental Law Clinic. Collins said that even if there is a lawsuit, plaintiffs might find it difficult to get their expert opinion into evidence, since the science isn’t clear.

The debate should be over anyway, say both state regulators and the drilling company Rex Energy, because multiple independent reviews found no contamination from drilling at all.

“In each case, the scientific analysis concluded that neither Rex Energy’s operations nor natural gas development impacted water quality,” said Rex spokesman Derek Smith, who noted that the company provided access to records, shared data, and gave “its complete cooperation and support” to the reviews. Rex is based in State College.

Yet Stoltz expects that ultimately his team’s research will provide a definitive answer for the Woodlands residents. The tests haven’t found any evidence of drilling chemicals in the water wells, but Stoltz said that even though no gas wells went directly under the Woodlands, the surrounding countryside is full of them. He said that while his team’s conclusions aren’t final, he believes that the recent gas drilling around the Woodlands has affected groundwater flows, thus indirectly causing problems for some people.

But even if drilling didn’t cause the problems, McIntyre said she doesn’t understand why the community must struggle to find the answer.

“It just seems like I can’t get some kind of justice,” she said. “I want water so bad I can taste it.”