Water

What Is Water?

Water (H₂O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom) is a transparent fluid which forms the world’s streams, lakes, oceans and rain. Water is a tasteless, odorless liquid at standard temperature and pressure. The color of water and ice is very slight blue hue, although water appears colorless in small quantities. Water vapor is essentially invisible as a gas.

The volume of water one Earth would be about 332,500,000 cubic miles or 1,386,000,000 cubic kilometers. Water also exists in the air as water vapor, lakes, rivers, icecaps, glaciers, soil moisture, atmosphere, aquifer, and even in human’s body. About 71% of the Earth’s surface is water-covered, and the oceans hold about 96.5% and freshwater has only about 3.5% of all Earth’s water. Over 68% of freshwater is locked up in ice and glaciers, and other 30% is underground water. Fresh surface-water sources, such as rivers and lakes, only constitute about 22,300 cubic miles (936,100 cubic kilometers), which is about 1/150^th of one percent of total water. he water is used for domestic, industrial, irrigation, livestock, mining, public supply, thermoelectric power, and aquaculture.

Terminology

Condensation: is the process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds.

Precipitation: is the water released from the clouds in the form of rain, freezing rain, sleet, snow, or hail. It is the primary connection in the water cycle that provides for the delivery of the atmospheric water to the Earth. Most precipitation falls as rain.

Evaporation: is the process by which water changes from liquid to a gas or vapor. Heat is necessary for evaporation to occur by breaking the bonds that hold water molecules together, which is why water easily evaporates at the boiling point (100°C), but evaporate much more slowly at the freezing point.

Open channel flow: is the flow with a free surface, such as flow in a river or in a partially full pipe.

Transpiration: is essentially evaporation of water from plant leaves. Studies have revealed that transpiration accounts for about 10% of the moisture in the atmosphere, with oceans, seas, and other water bodies providing nearly 90%, and a tiny sublimation.

Evapotranspiration: is the water lost to the atmosphere from the ground surface, evaporation from the capillary fringe of the groundwater table, and the transpiration of groundwater by plants whose roots tap the capillary fringe of the groundwater table.
Sublimation:  is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage.

Infiltration: is the process by which precipitation or water on ground surface enters the subsurface soils and moves into rocks through cracks and pore spaces.

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