Water entering an aquifer is known as recharge. The recharge comes from a variety of sources, including rain filtration and snow-melt, currents and groundwater flow from other areas. The recharge occurs when the permeable soil allows the water to seep into the soil. The areas where this occurs are called recharge areas. They may be small or large enough. A small recharge area can supply all the water to a large aquifer. The currents recharging the groundwater are called lost currents because they lose water to the surrounding soil or rock.
Groundwater begins with precipitation entering the soil. The amount of water infiltrating the soil will vary widely from place to place, depending on the slope of the land, the amount and intensity of precipitation and the type of land surface. Porous, or permeable, soil containing a lot of sand or gravel will allow up to 50 percent precipitation to seep into the soil and become groundwater. In less permeable areas, it can reach up to 5%. The remainder turns to runoff or evaporates. More than half of the fresh water on Earth is stored as groundwater. As the water seeps through permeable soil, it continues downward until it reaches a depth where the water has filled all the porous areas in the soil or rock. This is known as the saturated zone. The top of the saturated zone is called the water table. The water table can rise or fall according to the season of the year and the amount of precipitation that occurs.