Large amounts of water are stored in the ground. The water is still moving, possibly very slowly, and it is still part of the water cycle. Most of the water in the ground comes from precipitation that infiltrates downward from the land surface. The upper layer of the soil is the unsaturated zone, where water is present in varying amounts that change over time, but does not saturate the soil. Below this layer is the saturated zone, where all of the pores, cracks, and spaces between rock particles are saturated with water. The term ground water is used to describe this area. Another term for ground water is “aquifer,” although this term is usually used to describe water-bearing formations capable of yielding enough water to supply peoples’ uses. Aquifers are a huge storehouse of Earth’s water and people all over the world depend on ground water in their daily lives.

Even though the amount of water locked up in ground water is a small percentage of all of Earth’s water, it represents a large percentage of total freshwater on Earth. The pie chart shows that about 1.7 percent of all of Earth’s water is ground water and about 30.1 percent of all freshwater on Earth occurs as ground water.

[Via USGS]