I will say this. I support fracking and oil and gas extraction, but we should come up a way to treat this water instead of injecting it back. It might be more expensive, but it is getting impossible to ignore a very viable linkage between injection wells in this area and earthquakes.
They do have companies recycling hydro frac water. It is expensive and normally only done where there is significant expense to obtaining water in the first place. But water is also produce with oil and gas. Some wells will produce very little water. Some older wells might be 95% water; it can be too expensive to keep the oil flowing at that point.
The produced water is salty, along with hydrocarbons and other containments. It is injected back to deep reservoirs well below the fresh water layers.
Sometimes it is injected back at the edges of the same producing reservoir for enhanced oil recovery. That sweeps more fluid from the edges to the producing well, carrying with the water more oil.