Most of the water and additives used in hydraulic fracturing (or “fracking”) remain deep underground in the geologic formation from which the oil or gas is being extracted. But some of the fluid, mixed with water or brine from the formation, returns through the well to the surface and is referred to as “produced water”. After a well is brought on-line, large volumes of produced water (primarily composed of the injected fluid) are generated.
Produced water is often disposed of by injecting it into deep geologic formations via wells that are specifically designed for that purpose. In some cases, produced water can be treated and reused to hydraulically fracture another well. In other cases, the water is clean enough to meet regulatory standards and is discharged into local watersheds. Practices vary between regions, depending on regulations, geologic conditions, and water availability.