How much of the water used in horizontal hydrofracing is recovered?
If the frac job is done correctly, most, if not all, the volume of water used in hydrofracing is returned, but its composition changes over time as saline formation water begins to mix in with the frac water and is recovered with it. The time it takes to recover the frac water depends on whether there is enough gas to push the water out of the hole, or if the water needs to be pumped (initially) to get the gas to flow and carry out the rest. Generally it takes about two weeks to recover the volume of water initially injected; after that the water recovered is generally considered formation water.
How can homeowners protect their private well supplies?
Penn State has a bulletin Gas Well Drilling and Your Private Water Supply addressing this question.