This is a simple image of fracking, notice the bore hole goes through the water table and way below that the rock is fractured to release the gas. It seems reasonable to expect some damage to the ground water but the industry has denied it and tried to prevent the EPA from studying the dangers of fracking for years. After the fracking takes place, the waste sludge is injected into the earth, creating more risk to the ground water.
More on fracking in a diary by Joe Shikspack and I, 2012

From Inside Climate a Pulitzer Prize winning blog

Report Fuels Fracking Ban Push in California

The State of California Report, 2015:

The study's key takeaway is that "the state does not have adequate information to effectively regulate the process," said Andrew Grinberg, oil-and-gas program manager at the environmental group Clean Water Action. "To me, it is a clear indication that a moratorium is needed." [...]
It offers a snapshot of fracking in the state. Over the last decade, an average of 300 new oil wells have gone online per month and 125 to 175 of those are fracking wells. Unlike the fracking boom states like Texas, North Dakota, Colorado and Pennsylvania, California's fracking occurs at relatively shallow depths and involves less water per well.

But the study's assessment of current practices and recommendations has activists concerned. The analysis revealed that 36 percent of pits in the vast Central Valley operate without appropriate permits; it also exposed errors in the state regulator's reporting of wastewater disposal. And it identified how little is known about the impact or toxicity of 38 percent of the chemicals found in fracking fluids.[...]

[RL Miller is a Daily Kos contributor.
RL Miller, chair of the California Democratic Party's environmental caucus and founder of the Super PAC Climate Hawks Vote, is not impressed. Miller said Pavley's new amendment "is
really a way of saying that it's OK to keep fracking. And that's not what the activists want. Period. Full stop. We know that fracking is harmful to the climate and we know that fracking wastewater is not being handled well in California and we know that we don't know a real lot."

The Health Department of New York report, 2014:

called attention to "significant uncertainties" concerning fracking's threat to public health. The agency recommended a moratorium on the extraction method, which involves the injection of water, sand and chemicals into bedrock, under very high pressure, to release oil and gas.

In Canada, a ground-breaking law-suit will take place in 2016. I originally wrote about this in 2012 and these delays have cost the litigant time and money.

Supreme Court [of Canada] Rejects Argument to Dismiss Landmark Fracking Case
Eight years ago oil patch consultant Jessica Ernst sued Alberta Environment, the Energy Resources Conservation Board (ERCB, which has since become the Alberta Energy Regulator) and Encana -- one of Canada's largest unconventional gas drillers -- over the contamination of her well water with hydrocarbons (including methane) and the failure of government authorities to properly investigate the fouling of groundwater.

Industry, however, cannot always control the direction of the fractures and there have been hundreds of cases of groundwater contamination and methane leakage as well as scores of "felt" earthquakes triggered by the industry in Canada and the United States.

A list of Bans of Fracking Worldwide