This figure is from a paper by Fisher and Warpinski (2012). The wiggles at the bottom show the maximum heights of hydraulic fractures, as imaged by microseismic data. The upper blue lines shows the maximum depths of drinking-water aquifers in the areas.
This data shows clear separation of thousands of feet between drinking water sources and the rocks where hydraulic fracturing is being performed. This shows that hydraulic fracturing itself are extremely unlikely to be a cause of contamination - if water is impacted it is most likely to be from either spills at the surface or issues with wellbore integrity.