hydraulic fracturing uses between of water per well, with large projects using up to . additional water is used when wells are refractured. an average well requires of water over its lifetime. according to the oxford institute for energy studies, greater volumes of fracturing fluids are required in europe, where the shale depths average 1.5 times greater than in the u.s. surface water may be contaminated through spillage and improperly built and maintained waste pits, and ground water can be contaminated if the fluid is able to escape the formation being fractured (through, for example, abandoned wells, fractures, and faults) or by produced water (the returning fluids, which also contain dissolved constituents such as minerals and brine waters). the possibility of groundwater contamination from brine and fracturing fluid leakage through old abandoned wells is low. produced water is managed by underground injection, municipal and commercial wastewater treatment and discharge, self-contained systems at well sites or fields, and recycling to fracture future wells. typically less than half of the produced water used to fracture the formation is recovered.