Basic Facts about Water

It is everywhere around you: water covers about 70 per cent of the Earth’s surface, and there are around 1.4 billion cubic kilometres on our planet. The total amount does not change; it has stayed the same for millions of years.

However, only a fraction is available for human consumption. 97.5 per cent is in the oceans and salty; another 1.75 per cent is locked in icecaps and glaciers. The remaining freshwater is stored in lakes and rivers as well as in underground aquifers, although these are not always accessible for mining.

Freshwater availability Earth

Source: http://www.unep.org/dewa/vitalwater/article5.html

Around the world, an approximate total of 300 cubic kilometres of water a day fall from the sky onto land as rain, hail or snow  1. Unfortunately, this precipitation is not distributed evenly among everyone on Earth, and a large part of it immediately evaporates again (get more information on the water cycle).

Water and science

Water has some rather fascinating physical and chemical properties:

  • It is colourless (with a slight hint of blue), odourless as well as tasteless.
  • It is the only substance found naturally in all three forms – as a solid, a liquid, and a gas.
  • It has a (maximum) density of 1 g per cubic centimetre, meaning that 1 litre weighs 1 kg.
  • Its melting point is at 0° C (32° F) and it reaches boiling point at 100° C (212° F).
  • Its surface tension is high, which is why it forms drops instead of spreading out thinly.
  • 1 cubic metre is the equivalent of 1,000 litres.

Another unusual thing is that its density becomes highest at 4° C (39.2° F), which is above the melting point. This is the so-called density anomaly, and explains why solid water (ice), which is less dense, floats on top of its liquid form.

The molecular symbol for water is H2O. This means it consists of one oxygen bound to two hydrogen atoms.

Water is life

It is not difficult to understand why water is so important for humans, animals and plants. The average human body contains 60 per cent water. Your body loses around three litres every day, which you need to replenish by eating and drinking.


Seawater
 
Antarctic pack ice
 
Rain dropy in puddle
 
Water drops condensing on glass
 
Two school children drinking water from tap
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