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Water, a substance composed of the chemical elements hydrogen and oxygen and existing in gaseous, liquid, and solid states. It is one of the most plentiful and essential of compounds. A tasteless and odourless liquid at room temperature, it has the important ability to dissolve many other substances. Indeed, the versatility of water as a solvent is essential to living organisms. Life is believed to have originated in the aqueous solutions of the world’s oceans, and living organisms depend on aqueous solutions, such as blood and digestive juices, for biological processes. Water also exists on other planets and moons both within and beyond the solar system. In small quantities water appears colourless, but water actually has an intrinsic blue colour caused by slight absorption of light at red wavelengths.

Water cycle, also called hydrologic cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle remains essentially constant, its distribution among the various processes is continually changing.

Hydrosphere, discontinuous layer of water at or near Earth’s surface. It includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour.Water is the most abundant substance at the surface of Earth. About 1.4 billion cubic km (326 million cubic miles) of water in liquid and frozen form make up the oceans, lakes, streams, glaciers, and groundwaters found there. It is this enormous volume of water, in its various manifestations, that forms the discontinuous layer, enclosing much of the terrestrial surface, known as the hydrosphere.

The man and environment relationship can be studied under the following approaches.
Determinism − Friedrich Ratzel, the German geographer, was responsible for the development of the concepts of determinism, which was further expanded by Ellsworth Huntington.
This approach is based on the concept of ‘nature controls man’ or ‘earth made man’. According to this approach, man is largely influenced by nature. In fact, the determinism states that man is subordinate to natural environment because all aspects of human life such as physical (health and well-being), social, economic, political, ethical, aesthetic, etc. not only depend on but are dominantly controlled by the physical environment.
World famous biologist, Charles Darwin, in 1859 laid the foundation stone of the concept of environment influences on man and other organism.
Possibilism − Lucien Febvre, the French historian, founded the concept of Possibilism. Possibilism approach in the study of man-environment relationship is an offshoot of the criticism of environmental determinism and the impact of science and technology on such a relationship.
Possibilism indicates that the physical environment is passive and man is the active agent at liberty to choose between wide ranges of environmental possibilities. According to it, the pattern of human activity is the result of the initiative and mobility of man operating within the natural framework. Nowadays, the role of natural elements in conditioning, though not controlling human activities, is often lost sight of.