The correct answer is that chemicals added to the liquid can contaminate groundwater.
Fracking is a method of drilling fossil energy resources, which requires a lot of water and consumes local water resources. It is pumped with high pressure water, sand and chemicals, causing high pressure to block the porous rock and release gas.
The water spill itself destroys nature from the drilling site, and may even cause earthquakes, especially due to the pumping of abundant wastewater into porous rock types such as limestone. For example, Oklahoma appears to have become a special earthquake risk area. The biggest impact of water distortion is on groundwater. In Wyoming, USA, the same chemicals found in groundwater have been found in groundwater, and some of them are toxic or carcinogenic.