Storages are used to hold water for varying periods. In regulated river systems, storages control the supply of water to consumptive and non-consumptive users, and may also provide flood mitigation, social and environmental services. In a river model, they represent places where water is stored along the river, such as dams, reservoirs, weirs and wetlands. Storages operate by maintaining water mass balance. Water can also be 'in transit' along a reach (link) in the case of storage routing.  

Typically, inflows to storages include stream flow from upstream catchments, rainfall over the storage surface area, recharge from groundwater, and runoff from the local catchment surrounding the storage. Outflows from storages include controlled releases and spills. Losses from storages include evaporation from the storage surface area and seepage to groundwater.