In the liquid form, the hydrogen atoms of one water molecule are attracted to the oxygen atom of another molecule. Each water molecule can form up to four of these hydrogen bonds and, collectively, they give water a cohesiveness unique in liquids.

Water’s extensive capability to dissolve a variety of molecules has earned it the designation of “universal solvent,” and it is this ability that makes water such an invaluable life-sustaining force. On a biological level, water’s role as a solvent helps cells transport and use substances like oxygen or nutrients.

Non-water based liquids like cooking oils, kerosene, mineral turpentine, paraffin oil and oil based paints are less frequently identified. Evidence suggests that students freely associate liquids with water or assume they all contain some water because they are a liquid.

Water is the only common substance that is naturally found as a solid, liquid or gas. Solids, liquids and gases are known as states of matter. This animation explores water as a solid, liquid and gas. The water molecules stay the same, but they behave differently as they change from one form to another.

Water is simple enough, but not too simple. This means that one possibility for explaining the apparent extra phase of water is that it behaves a little bit like a liquid crystal.

Water is, by far, the most common liquid on Earth. The density of a liquid is usually close to that of a solid, and much higher than in a gas. Therefore, liquid and solid are both termed condensed matter.

Examples of Liquids

• Water.
• Milk.
• Blood.
• Urine.
• Gasoline.
• Mercury (an element)
• Bromine (an element)
• Wine.

• Bose–Einstein condensate.
• Fermionic condensate.
• Degenerate matter.
• Quantum Hall.
• Rydberg matter.
• Rydberg polaron.
• Strange matter.
• Superfluid.

A liquid is matter that has a definite size but does not have a definite shape.

No liquid can be completely stable in a vacuum, since all liquids have some non-zero vapour pressure, and so will evaporate at some rate. However some liquids have an exceptionally low vapour pressure, and so can be used in a vacuum.

A water drop and air bubble in outer space. Consider what would happen on Earth: The air bubble, lighter than water, would race upward to burst through the surface of the droplet. In space, the air bubble doesn’t rise because it is no lighter than the water around it—there’s no buoyancy.

In a vacuum chamber, the pressure can be extremely low. So low, in fact, that water can actually boil at room temperature. So, if you put some water in a high-vacuum chamber you will see it boil.

Water is abundant in space and is made up of hydrogen created in the Big Bang and oxygen released from dying stars. The planets of our solar system were created around 4.6 billion years ago from clumps of rocks spinning around the Sun. So, according to the textbooks, water must have come later.

Is it possible to make water? Theoretically, it is possible. You would need to combine two moles of hydrogen gas and one mole of oxygen gas to turn them into water. However, you need activation energy to join them together and start the reaction.

In our own solar system, Earth is the only planet with liquid water on its surface. But in a study of more than 4000 exoplanets, a team led by Li Zeng, a planetary scientist at Harvard University in the US, found that fully 35% appear to contain up to half their mass as water.

3.8 billion years ago

Though water itself doesn’t expire, bottled water often has an expiration date. This is because plastic can begin to leach into the water over time, contaminating it with chemicals, such as antimony and bisphenol A (BPA) ( 5 , 6 , 7 ).

about 18 hours and 40 minutes

They indicate that 620 million years ago the day was 21 hours, says Dr Mardling. Since the dinosaurs lived during the Mesozoic era, from 250 million years ago to 65 million years ago, day length would have been longer than this — probably closer to 23 hours.

about 65 million years ago

23 hours

23 hours and 56 minutes