Aqueduct, (from Latin aqua + ducere, “to lead water”), conduit built to convey water. In a restricted sense, aqueducts are structures…

Water cycle, also called hydrologic cycle, cycle that involves the continuous circulation of water in the…

Groundwater, water that occurs below the surface of Earth, where it occupies all or part of the void…

Indus River, Tibetan and Sanskrit Sindhu, Sindhi Sindhu, or Mehran, great trans-Himalayan river of South Asia. It is one of the…

Aquifer Aquifer, in hydrology, rock layer that contains water and releases it in appreciable amounts. The rock contains water-filled pore…

Firefighting, activity directed at limiting the spread of fire and extinguishing it, particularly as performed…

Irrigation and drainage, artificial application of water to land and artificial removal of excess water from land,…

General nature of the cycle The present-day water cycle at Earth’s surface is made up of several parts. Some…

Chemical element, also called element, any substance that cannot be decomposed into simpler substances by ordinary…

Liquid water The water molecule is composed of two hydrogen atoms, each linked by a single chemical bond to an oxygen atom. Most hydrogen atoms…