The hydrological or water cycle is the constant recycling of water in the earth system. Water that we drink today is the same water the dinosaurs drank. The water cycle consists of evaporation, condensation, evapotranspiration, and precipitation. Evaporation puts water into the atmosphere by changing liquid water to water vapor. This comes from lakes, rivers, and the oceans. Condensation occurs as water vapor changes to liquid water in the form of clouds. Evapotranspiration puts water into the atmosphere from the plants and trees on earth. Precipitation returns water to the surface of the earth. On the surface of the earth the water may run off into streams, lakes, rivers, and oceans or may seep into the earth and replenish stores of groundwater.
The Global Hydrological Cycle might be more simply referred to as the water cycle. This is the process by which water circulates throughout the globe. Here is a very basic description of this cycle. Water evaporates from the oceans, streams, and other bodies of water. It condenses in the atmosphere as clouds. The clouds then distribute the water as precipitation. Many things affect this water cycle and alter the way it affects our globe. For instance, pollutants in the air can be gathered in precipitation. This leads to problems like acid rain. For more information on such events, check out the Global Energy and Water Cycle Experiment.