Hydrology is the science that has to do with water on our planet and in the atmosphere, including how water moves, where it exists, and its specific properties.
Hydrology is a branch of geology, the study of the Earth, that focuses specifically on the planet's water systems. This scientific specialization involves analysis of our water's quantity, quality, and location based on the water cycle. Scientists who study hydrology are known as hydrologists, and their work includes testing water samples for contamination, predicting floods and droughts, and making sure our drinking water is clean. The word hydrology comes from the Greek roots hydro-, meaning "water," and -logy, meaning "study of."