In the 2015 Oil and Gas Annual Report put out by the Pennsylvania Department of Environmental Protection, no new cases of contaminated drinking water resulting from oil and gas operations, also called “stray gas cases,” were recorded.

Pittsburgh Post-Gazette PowerSource reports that oil and gas companies have been working to reduce the number of stray gas cases. Improved well construction rules and more attention paid to seismic data before drilling has helped to decrease the number of stray gas cases.

In 2010, there were 28 stray gas cases that affected 57 water supplies in Pennsylvania. Since 2007, 281 drinking water supplies have been affected by Pennsylvania oil and gas operations. That number includes both pollution cases and instances of reduced flow to taps, according to the source.

Read more: Pittsburgh Post-Gazette PowerSource > Cases of drilling sending gas into water supplies declines in Pennsylvania