Water
From
Wikipedia, the free encyclopedia.
Water in
three states: liquid, solid (ice), and gas (invisible water vapor in the air).
Water is a
transparent and nearly colorless chemical substance that is the main
constituent of Earth's streams, lakes, and oceans, and the fluids of most
living organisms. Its chemical formula is H2O, meaning that its molecule
contains one oxygen and two hydrogen atoms, that are connected by covalent
bonds. Water strictly refers to the liquid state of that substance, that
prevails at standard ambient temperature and pressure; but it often refers also
to its solid state (ice) or its gaseous state (steam or water vapor). It also
occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew,
aquifers, and atmospheric humidity.
Water
covers 71% of the Earth's surface. It is vital for all known forms of life.
On Earth, 96.5% of the planet's crust water is found in seas and oceans, 1.7%
in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland,
a small fraction in other large water bodies, and 0.001% in the air as vapor,
clouds (formed of ice and liquid water suspended in air), and
precipitation. Only 2.5% of this water is freshwater, and 98.8% of that
water is in ice (excepting ice in clouds) and groundwater. Less than 0.3% of
all freshwater is in rivers, lakes, and the atmosphere, and an even smaller
amount of the Earth's freshwater (0.003%) is contained within biological bodies
and manufactured products. A greater quantity of water is found in the
earth's interior.
Water on
Earth moves continually through the water cycle of evaporation and
transpiration (evapotranspiration), condensation, precipitation, and runoff,
usually reaching the sea. Evaporation and transpiration contribute to the
precipitation over land. Large amounts of water are also chemically combined or
adsorbed in hydrated minerals.
Safe
drinking water is essential to humans and other lifeforms even though it
provides no calories or organic nutrients. Access to safe drinking water has
improved over the last decades in almost every part of the world, but
approximately one billion people still lack access to safe water and over 2.5
billion lack access to adequate sanitation. There is a clear correlation
between access to safe water and gross domestic product per capita.[6] However,
some observers have estimated that by 2025 more than half of the world population
will be facing water-based vulnerability. A report, issued in November 2009,
suggests that by 2030, in some developing regions of the world, water demand
will exceed supply by 50%.
Water plays
an important role in the world economy. Approximately 70% of the freshwater
used by humans goes to agriculture. Fishing in salt and fresh water bodies
is a major source of food for many parts of the world. Much of long-distance
trade of commodities (such as oil and natural gas) and manufactured products is
transported by boats through seas, rivers, lakes, and canals. Large quantities
of water, ice, and steam are used for cooling and heating, in industry and
homes. Water is an excellent solvent for a wide variety of chemical substances;
as such it is widely used in industrial processes, and in cooking and washing.
Water is also central to many sports and other forms of entertainment, such as
swimming, pleasure boating, boat racing, surfing, sport fishing, and diving.
Inga kommentarer:
Skicka en kommentar