A new study suggests that the contamination of drinking water by shale gas is due to faulty wells and not hydraulic fracturing. Researchers in the US analysed the gas content in 130 water wells in Pennsylvania and Texas. They were able to trace the methane found in the water to problems with the casing or lining of wells drilled to extract the gas. The report appears in the Proceedings of the National Academy of Sciences. In many parts of the US, the migration of gas into drinking water has raised questions about the fracking process.