Hydrology is the study of water on Earth, including the hydrologic cycle, water resources, and sustainability. It involves the movement and distribution of water throughout the planet. The main domains of hydrology include surface water, groundwater, drainage basins, and water quality. Precipitation, evaporation, soil water, aquifers, floods, and water reservoirs are some of the key concepts and topics in hydrology. Major damage from floods globally costs billions of dollars annually.