The hydrologic watercycle is the water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere. Water evaporates from the earth and rises into the atmosphere where it forms clouds. In nature, this is where water is in its purest form. However, it does not stay that way for long. Its stay in the air is short. Water droplets forming in clouds, absorb particles and impurities found floating in the air. Click on the image tab to see a pictoral of the cycle.