What is water?

  • Water has the chemical formula H2O.  This means there are two hydrogen (H) atoms for every one oxygen (O) atom

  • It is colourless, tasteless, odourless and is a liquid at room temperature (this is 25°C) and pressure (this is 1 atmosphere).  

  • Water boils at 100°C and freezes at 0°C.  

  • Frozen water is 9% lighter than liquid water which is why it floats.  

  • Water may exist as a liquid (water), vapour/gas (evaporation) and solid (ice) and at certain temperatures and pressures it can exist in all three states at the same time.  

  • Water is the ONLY substance on Earth to naturally exist in all three states (solid, liquid and gas).  Other substances can exist in these states but must be forced to do so by artificial means.

  • About 70% of the Earth surface is covered in water which is why the Earth is known as the ‘blue planet’ and humans are made up of approximately 70% water.  So water is important to our Earth and to our lives.  Without water there would not be a water cycle (refer to section on Water Cycle for further information) and without the water cycle the Earth would quickly become dry and have no plant or animal life.