Penn State School of Forest Resources has a document titled “Gas Well Drilling and Your Private Water Supply“. It explains how gas well drilling and gas wells might create issues with a private water supply. This matter has become a concern in Pennsylvania because of the Marcellus Shale gas drilling.
A relevant quote from the document: “Contamination of private wells and springs can occur from gas well drilling but it is not common. Data from various regulatory agencies responsible for enforcement
of gas well drilling regulations indicate that more than 95% of complaints received by homeowners suspecting problems from nearby gas well drilling are, instead, due to pre-existing problems or other land use activities.”