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.
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada. It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean. The river is 1,243 miles (2,000 km) long, and its largest tributary is the Snake River. Its drainage basin is roughly the size of France and extends into seven US states and a Canadian province. The fourth-largest river in the United States by volume, the Columbia has the greatest flow of any North American river entering the Pacific.
The Columbia and its tributaries have been central to the region's culture and economy for thousands of years. They have been used for transportation since ancient times, linking the region's many cultural groups. The river system hosts many species of anadromous fish, which migrate between freshwater habitats and the saline waters of the Pacific Ocean. These fish—especially the salmon species—provided the core subsistence for native peoples.
In the late 18th century, a private American ship became the first non-indigenous vessel to enter the river; it was followed by a British explorer, who navigated past the Oregon Coast Range into the Willamette Valley. In the following decades, fur trading companies used the Columbia as a key transportation route. Overland explorers entered the Willamette Valley through the scenic but treacherous Columbia River Gorge, and pioneers began to settle the valley in increasing numbers. Steamships along the river linked communities and facilitated trade; the arrival of railroads in the late 19th century, many running along the river, supplemented these links.
Since the late 19th century, public and private sectors have heavily developed the river. To aid ship and barge navigation, locks have been built along the lower Columbia and its tributaries, and dredging has opened, maintained, and enlarged shipping channels. Since the early 20th century, dams have been built across the river for power generation, navigation, irrigation, and flood control. The 14 hydroelectric dams on the Columbia's main stem and many more on its tributaries produce more than 44 percent of total US hydroelectric generation. Production of nuclear power has taken place at two sites along the river. Plutonium for nuclear weapons was produced for decades at the Hanford Site, which is now the most contaminated nuclear site in the US. These developments have greatly altered river environments in the watershed, mainly through industrial pollution and barriers to fish migration. 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
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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.