Water in two states: liquid (including the clouds, which are examples of aerosols
), and solid (ice
Water is a transparent, tasteless, odorless, 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 each of its molecules contains one oxygen and two hydrogen atoms that are connected by covalent bonds. Strictly speaking, water refers to the liquid state of a 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. 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.
Satellite photo from August 2003 after five years of drought
, reaching near-record lows. Note the difference in colors between the northern and southern portions of the lake, the result of a railroad causeway
The Great Salt Lake, located in the northern part of the U.S. state of Utah, is the largest salt water lake in the Western Hemisphere, and the eighth-largest terminal lake in the world. In an average year the lake covers an area of around 1,700 square miles (4,400 km2), but the lake's size fluctuates substantially due to its shallowness. For instance, in 1963 it reached its lowest recorded size at 950 square miles (2,460 km²), but in 1988 the surface area was at the historic high of 3,300 square miles (8,500 km2). In terms of surface area, it is the largest lake in the United States that is not part of the Great Lakes region.
The lake is the largest remnant of Lake Bonneville, a prehistoric pluvial lake that once covered much of western Utah. The three major tributaries to the lake, the Jordan, Weber, and Bear rivers together deposit around 1.1 million tons of minerals in the lake each year. As it is endorheic (has no outlet besides evaporation), it has very high salinity (far saltier than seawater) and its mineral content is steadily increasing. Due to the high density resulting from its mineral content, swimming in the Great Salt Lake is similar to floating. Its shallow, warm waters cause frequent, sometimes heavy lake-effect snows from late fall through spring.
Although it has been called "America's Dead Sea", the lake provides habitat for millions of native birds, brine shrimp, shorebirds, and waterfowl, including the largest staging population of Wilson's phalarope in the world. Read more...
Did you know...
... that the International Water Management Institute celebrated its 25th anniversary last year?
... that the International Water Centre celebrated its 5th birthday last year?
... that the National Rural Water Association represents more than 26,242 water and wastewater utility members?
... that "water bears" are small, segmented animals that can survive in a dehydrated state for nearly 10 years?
... that there are at least 15 different forms of crystalline ice?
... that water memory is a controversial homeopathic concept, which holds that water is capable of containing "memory" of particles dissolved in it?
... that there are more particles in a glass of water than grains of sand on earth?
... that there is a new definition for Earth's water cycle that includes the three "interactive"
cycles: cosmic water cycle; atmospheric water cycle, and oceanic water cycle (new ocean
recycled from center of Earth about every 7 million years) The Water Channel TV
- "The Arizona Court of Appeals recently upheld a decision that the Arizona Department of Water Resources has the right to issue instream flow permits and affirmed the principle that instream flow and in situ water rights need not be diversionary." 
- The World Water Assessment Programme monitors freshwater issues and provides recommendations
- The Source Water and Sanitation News Service provides news in English, French and Spanish with an emphasis on rural and peri-urban areas in developing countries
- UNESCO Water Portal and weekly newsletter
- Dundee UNESCO Centre a portal for Water Law, Policy and Science from the University of Dundee
- Water Planning Tools - news, reviews and updates for water planners and managers, Australia
-  - [The Water Network - knowledge platform for the Water professionals to connect share knowledge.Switzerland
- Global Water News Watch, from SAHRA in Arizona USA
- U.S. Water Monitor - a portal to federal water information
- Watershed News from U.S. Environmental Protection Agency
- USDA Soil Conservation Service website news
- National Rural Water Association NRWA news and press releases
- The 2005 Preliminary Report of the Sustainable Water Resources Roundtable (SWRR) is now available.
- India Water Portal Community-contributed water resources, articles, news, Q&A, data, events, opportunities, photos and videos.
- Alberta WaterPortal Water news, info, events, and community.
Things you can do
See Category:Water for complete list.
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- WikiProject Lakes describes the Earth's lakes. The project aims to consolidate and unify pages relating to lakes around the world.