What is fracking? Here’s the short answer: Hydraulic fracturing, also known as fracking, is a drilling practice that calls for injecting millions of gallons of a toxic mixture of chemicals, water and sand into the earth in order to create enough pressure to cracks open rocks and release oil or natural gas. And here’s what you need to know: 1. The nearly 600 chemicals used in fracking include known carcinogens such as benzene, toluene, ethyl benzene and xylene, among others, which can leach into drinking water.