The hydrologic cycle is the process of water’s movement over the entire Earth and below the earth’s surface. Water is constantly changing state, from liquid to vapor to ice and back again, over the course of what can span milliseconds to millions of years.
The cycle is a complex process, comprising several stages and components including:
- Atmosphere – According to some estimates, the volume of water in the atmosphere at any one time is about 3,100 cubic miles, or approximately 0.001 percent of the Earth’s total water volume of roughly 332,500,000 cubic miles.
- Freshwater – Containing less than 1,000 milligrams per liter of dissolved solids (usually salt), surface freshwater includes streams, ponds, lakes, reservoirs and canals, and freshwater wetlands.
- Saltwater – Approximately 71 percent of the Earth’s surface is water and roughly 97 percent of that water is saltwater in the form of oceans, lakes, and seas.
- Aquifer – A geological water-bearing formation or structure that stores and/or transmits water to wells and springs; capable of yielding water in sufficient quantity to constitute a usable supply.
- Groundwater – Water that flows or seeps downward and saturates soil or rock, supplying springs and wells.
- Springs – The result of an aquifer filled to the point that the water overflows onto the surface. A spring is formed when the side of a hill or valley bottom intersects a flowing body of groundwater at or below the local water table.