The hydrologic cycle, sometimes called the water cycle, is the movement of water between the air, land and bodies of water. The hydrologic cycle includes numerous physical, chemical and biological processes. Almost 98% of the water on Earth is in liquid form. The rest is either bound up in ice, in the soil, in living organisms, or in the atmosphere. The hydrologic cycle is balanced on Earth because any water moving out of an environment is balanced by water moving in.

The hydrologic cycle also shows how water moves from one state to another. Evaporation is the changing of water from a liquid state to a gaseous state. Because of the heat of the sun, water evaporates from oceans, lakes, ponds, rivers, streams and glaciers and enters the atmosphere as gaseous water vapor. A small amount of water evaporates from the soil surface. In addition, water enters...