Water is a chemical compound that consists of one oxygen molecule and two hydrogen_ molecules.


1   Substance

Most water is not pure. 97% of water on Earth is saltwater_; only 3% is freshwater_.

2   Function

Water is an essential nutrient for all known forms of life.

Agriculture accounts for 80% of all water usage. Industrial accounts for 10%. Drinking water is about 5%.

3   Forms

Cumulus clouds weigh 1.1 million pounds.

4   Water treatment

Water treatment is any process that improves the quality of water to make it appropriate for a specific use.

4.1   Purification

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water.

4.2   Desalination

Desalination is water treatment that separates dissolved salts from water.

Desalination requires a lot of energy. It's almost always cheaper to use local freshwater than to desalinate seawater.

5   Properties

5.2   Opacity

Why is the ocean sometimes really dark like in the north Atlantic yet in some places a turquoise color like in the Caribbean?

It’s because dead animals and plants sink in water. That might seem obvious, but it means that any nutrients in sea water are rapidly used up by animals and plants and when those organisms die they sink to the bottom taking the nutrients with them. The only way those lost nutrients can be replaced is if water from the ocean bottom, where all those dead organisms go, can be moved to the surface again.

That cycling can't happen in warmer regions because the surface water is warm and warm water floats on the cold water of the ocean bottom. As a result warmer waters very rapidly become nutrient deficient.

Because they are nutrient deficient very little actually lives in tropical waters. Very few algae, very little plankton and so forth. And because nothing much lives in tropical waters they remain clear. That means that light can get way down into the depths, and as light passes through the water the blue wavelengths get scattered. That produces a vivid turquoise blue ocean.

In contrast cold waters are dirty and full of life due to the upwelling of water from the ocean bottom. All that dirt and all the life it supports absorbs sunlight very fast. Light will only penetrate a few meters in cold waters. With very little penetration the light also doesn’t have much chance to scatter. That produces an ocean that is very dark colored, and where the blue wavelengths are muted by the reds and greens to produce a muddy blue-gray.

5.3   Specific heat

It's also important to remember the difference between a Continental Climate and a Coastal Climate. The further you get from large bodies of water, the more extreme the temperatures become on both sides (the hotter your summer and colder your winter). This is because large bodies of water act as thermal regulators for weather.

Water has a high specific heat, higher than most things. It takes more energy to raise the temperature of water than it does land. So water heats slower than land, meaning when it's very hot, the surface of the water is cooler than the surroundings. The water cools the air, which cools the land near it in the summer.

Water is also an amazing insulator. It loses heat slower than its surroundings. Also the ocean is salt water, so it has a lower freezing point than water on land. Ocean water can get cooler than fresh water and stay liquid, allowing it to continue to redistribute heat through convection. So water is generally warmer than the land during the winter, creating warmer air around it.

5.4   Viscosity

Viscosity is a measure of its resistance to gradual deformation by shear stress or tensile stress.[

6   Market

6.1   Bottled water

Attitudes began to shift in the 1970s, when Europe’s Perrier set its sights on the American market. In 1977, the company spent $5 million on an advertising campaign in New York, selling itself as a chic, upscale product. Yuppies lapped it up. “It was a lifestyle-defining product,” Chapelle says. By 1982, U.S. bottled-water consumption had doubled to 3.4 gallons per person per year. [1]

Seeing an opportunity, U.S. beverage producers followed Perrier’s lead. In 1994, Pepsi launched Aquafina. Coca-Cola joined the club with Dasani in 1999. Homegrown brands, though, couldn’t boast glamorous European roots. So instead, they made Americans afraid of the tap. One ad from Royal Spring Water claimed that “tap water is poison.” Another, from Calistoga Mountain Spring Water, asked: “How can you be sure your water is safe? . . . Unfortunately, you can’t.” Fiji Water infuriated Ohio with the tagline “The label says Fiji because it’s not bottled in Cleveland.” The insinuation, of course, was that there was something wrong with local water. [1]

6.2   Carbonated drinks

Club soda is water with mineral-like ingredients such as `sodium bicarbonate`_, `sodium citrate`_, and `potassium sulfate`_. It's unflavored other than a mineral state, and is usually used to mix cocktails.

Seltzer is plain water with carbon dioxide added, often sweetened and flavored with citrus or other fruits.

Sparkling water usual comes from a natural spring or well, which may provide natural carbonation.

Tonic water is carbonated water that includes quinine, an ingredient ofund in the bark of the South American cinchona tree. Quinine was originally used as malaria medicine, and was mixed with sugar and gin to make it go down easier.

In fact, Valtin found that the 8 x 8 guideline may have originated from a misunderstanding.

7   References

[1](1, 2) http://www.washingtonpost.com/opinions/we-dont-trust-drinking-fountains-anymore-and-thats-bad-for-our-health/2015/07/02/24eca9bc-15f0-11e5-9ddc-e3353542100c_story.html

When ponds dry up and fish/other aquatic animals die, how does life return to the pond when it fills back up? Many aquatic animals are able to lay eggs that can dry up and go dormant until they get rehydrated again. Algae leaves spores that do the same.

The idea that ice is slippery because of water on its surface had been around for a long time but wasn't convincingly proved until 1987.

Why does water expand when it's frozen?