Groundwater recharge is the process of water being absorbed into the ground from precipitation, snowmelt, or artificial processes. Intentional groundwater recharge uses large, open basins that allow water to slowly seep into the ground. This water is filtered by sediment while traveling underground and is pumped back to the surface as a source of freshwater. In California, groundwater accounts for around 41% of the state's total water supply,[1] although this number varies between wet and dry years. During years of greater than average rainfall, less groundwater is used to allow for reserves to be available during dry years. Up to 60% of all water can be sourced from groundwater during dry years. The amount of water in underground aquifers is carefully monitored by the State Water Resources Control Board and other regional water resource boards.[2]