The water we use today has been around for a long long time. That is because water can recycle itself in the water cycle, which is also called the hydrologic cycle. Let's start the cycle with the evaporation of water from the surface of the ocean. As this moist air is lifted, it cools and water vapour condenses. It may form clouds. In fact, clouds are made up of tiny water droplets and ice crystals that are so small they can float in the air. This moisture in the atmosphere may be transported around the globe until it returns to the surface as precipitation. Precipitation may take the form of rain, snow, sleet or hail. Now once this water reaches the ground, one or two processes may occur. Some of the water may evaporate back into the atmosphere, or the water may penetrate the surface and become groundwater. The groundwater may take several different paths. The groundwater may seep in its way into the oceans river or streams, or it may go into an aquifer, which is a body of saturated walk rock through which water can easily move, or it may be released back into the atmosphere through transpiration. Transpiration occurs when leaves from trees and other vegetation give off water vapor through pores in their leaves. Some water on the Earth's surface is not absorbed by plants or become ground water, and it becomes surface runoff. This runoff may empty into lakes, rivers, and streams and then is carried back to the ocean where the cycle may begin.