Pressure on freshwater supplies will increase to meet anticipated needs for municipal and industrial uses, agricultural irrigation, and environment protection in the coming years. Certain conditions such as increasing population, changing land use, reallocation of existing water resources, reduction of snowpack, and overdrafting of aquifers will require tapping into other non-traditional sources of water. While other water management strategies have been used to increase freshwater supply through importation or desalination, improving water efficiency through technology and conservation, and reuse of treated wastewater, the potential for managed underground systems to sustain future water supplies is considerable.

With or without the other strategies, there is already a need for temporary detention and storage of water during times of abundance and recovery that water in times of scarcity. The traditional practice of storing water aboveground has been met with several challenges such as evaporative losses, sediment accumulation, land consumption, high cost, and ecological impact. Because of these factors there is increasing interest in storing recoverable water underground as part of a larger water management strategy. This has brought with it, however, its own set of challenges, such as costs to design, construct, and monitor the system; loss of some percentage of the water; chemical reactions with aquifer materials; ownership issues; and environmental impacts.

The source water for underground storage may come from streams or groundwater, water reclamation plants, or other sources and be recharged through different methods. After recovery, it may be used for potable, industrial, agricultural, environmental, and other purposes. For this report, the term managed underground storage (MUS) is