John Sullivan of the Boston Water and Sewer Commission testified that since September 11 the nation's drinking water utilities have been on a heightened state of alert to protect against the potential disruption of water service and biological or chemical contamination of drinking water.

CNN: FBI: 'No specific, credible threats' to drinking water

Some scientists have proposed adding chemical tracers to fracking fluids as a way of confirming that any contamination of drinking water comes from the drilling process.

BBC: Fracking: Untangling fact from fiction