Percolation is part of the water cycle that occurs after precipitation and before storage during which water filters down through aerated soil due to gravity. After percolation, water is stored in groundwater reservoirs until it reaches a point where sunlight warms it and the water evaporates. Much like a coffeemaker percolates water from top to bottom, water percolates down through soil until it reaches the water table.
Water percolating in aerated soil is called vadose water, and water that reaches the saturated part of soil is groundwater. The boundary between vadose water and groundwater is called the water table. Percolating water replenishes aquifers, huge underground reservoirs filled with water.
Groundwater reaches the surface through subterranean movement, which is the type of movement that occurs in springs. A spring is a hole in the ground that meets the upper level of an aquifer, which may form a stream. Water from the stream may flow back into the spring if relative water level conditions are right.
Scientists believe accessible groundwater accounts for 0.31 percent of the Earth's total water involved in the water cycle, and freshwater is approximately 2.90 percent of the Earth's water by volume. Most of the water on Earth, 97 percent, exists as salt water in the oceans. Just 0.10 percent of the water on the planet is in the atmosphere.