Researchers at the Duke University have warned that the controversial technique of shale gas drilling raises the risk of near drinking water becoming contaminated with methane.

Samples taken from water wells within 1,000 feet of a natural gas drilling sites showed, on average, 17 times higher concentration of methane gas.

Co-author Rob Jackson, Nicholas Professor of Global Change at Duke University, said that they found shocking levels of methane in water wells that were close to natural gas wells.

Commenting on the topic, "We found that within a kilometre of an active gas well, you were much more likely to have high methane concentrations."

Growing demand for energy has provided an unprecedented boost to the shale gas extraction across the world, prompting concerns regarding the impact of the controversial technology.

There are some videos available on the Internet that show people setting fire to water coming out of a tap. Prof Jackson also claimed that he himself had witnessed such a spectacle.

Shale natural gas contains around 90 per cent methane, which is odorless, tasteless and colorless. It is explosive and can cause asphyxiation.