hydrology

n. study of the properties and distribution of water on the earth and in the atmosphere

Hydrology (from Greek: Yδωρ, hudōr, "water"; and λόγος, logos, "knowledge") is the study of the movement, distribution, and quality of water throughout the Earth, and thus addresses both the hydrologic cycle and water resources. A practitioner of hydrology is a hydrologist, working within the fields of either earth or environmental science, physical geography or civil and environmental engineering.
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Noun
1. the branch of geology that studies water on the earth and in the atmosphere: its distribution and uses and conservation
(hypernym) geophysics, geophysical science

(n.)
The science of water, its properties, phenomena, and distribution over the earth's surface.
  

The science dealing with the properties, distribution, and circulation of water.