Minutes after Debby Kline flicked a lighter near a bathroom sink in her Portage County house in northeastern Ohio, she called the fire department.

A sink-to-ceiling flare erupted when she tried to light a candle on Dec. 21, she told a TV news show. State oil and gas regulators are still investigating what caused natural gas to bubble out of the faucet.

Kline’s Nelson Township house is within a half-mile of two Utica shale wells that state records show were drilled and fracked in October and November.

Videos of burning water in Ohio and Pennsylvania households have helped bring attention to shale drilling and fracking, but such incidents are rare. Most complaints associated with oil and gas drilling are about drinking-water wells that run dry or produce water that’s discolored, smelly or clogged with sediment.

But in some cases, natural gas from poorly cased and cemented wells can seep into drinking-water wells, making faucets spit fizzy water that some homeowners can ignite.

“We encourage people not to do that, because there is an explosive risk,” said Kevin Sunday, a spokesman for the Pennsylvania Department of Environmental Protection.

Ohio Department of Natural Resources officials said they could not discuss Kline’s case while it is being investigated. Kline also declined to comment.

Oil- and gas-industry advocates say shallow pockets of natural gas can leak into groundwater. They say drilling gets blamed for something that has been going on, unnoticed, for years.

“You’ll find that is the case up and down eastern Ohio and West Virginia and Pennsylvania,” said Tom Stewart, vice president of the Ohio Oil and Gas Association.

The drinking-water problems in Ohio and Pennsylvania do not stem from fracking, a process that injects millions of tons of water, sand and chemicals underground to shatter shale and free trapped oil and gas. Instead, most involve spills or leaks from drill sites that contaminate drinking-water wells, and shale wells that are not properly cased in cement and steel during drilling.

Although combustible water is rare, the number of drinking-water complaints has increased since shale drilling and fracking began. Natural Resources investigated 37 complaints in 2010, 54 in 2011 and 61 last year. The complaints include those about new conventional oil and gas drilling as well as leaks from wells drilled decades ago.

Since 2010, the agency has found four cases in which drinking water was polluted by oil and gas wells and drilling. However, none of the four cases involved shale drilling, said Mark Bruce, a spokesman for the Natural Resources Department.

In August 2011, the state found high concentrations of salt contaminating Carol Buck’s drinking-water well in Brown Township, Carroll County, in northeastern Ohio. Investigators linked it to brine that leaked from a nearby drilling rig’s temporary disposal pit.

EnerVest, the Houston-based drilling company, supplied Buck with water until October 2011, when tests showed the salt had dissipated.

Pennsylvania has investigated 969 complaints there since fracking began in 2008. Drilling and spills from rigs and oil and gas wells were linked to 106 of those complaints.

Natural Resources encourages homeowners to have their water tested for methane and other contaminants before drilling begins, Bruce said. The state also requires drilling companies to test drinking-water wells within 1,500 feet of their planned drilling sites. If pollution or contamination is there, those pre-drilling results will confirm it.

“If you don’t have that base line, it makes it much more difficult to do an investigation,” Bruce said.