Surface water evaporates from by energy of the sun. The water vapor then forms clouds in the sky. Depending on the temperature and weather conditions, the water vapor condenses and falls to the earth as different types of precipitation (rain, snow, sleet, hail). Some precipitation moves from high areas to low areas on the earth's surface and into surface water bodies. This is known as surface runoff. Other precipitation seeps into the ground and is stored as groundwater.