What is water?

  • Water is a compound of two elements: hydrogen and oxygen.

  • Water has many special properties.

  • Water is vital to all plant and animal life on Earth.

What is water?

Inside a water molecule

Water exists as molecules. Each molecule is made up of two hydrogen atoms joined to one oxygen atom. This means that the chemical formula of water is H₂O.

A water molecule is made up of two hydrogen atoms joined to one oxygen atom.
A water molecule is made up of two hydrogen atoms joined to one oxygen atom.

Why is water special?

Water covers more than 70% of the Earth’s surface. The most common locations are in oceans, rivers, lakes and glaciers.

It has special properties:

  • It exists in the solid, liquid and gas states at normal temperatures on Earth.

  • At 4°C water is at its most dense. Below this temperature, ice is able to float on liquid water.

  • Water dissolves many substances, including salts in the sea and proteins in living things.

  • Water has a high surface tension, allowing some small insects to walk on its surface.

Picture of water in its ice and water state and a depiction of materials in solid, liquid and gas states.
Water can exist in solid, liquid and gas states at normal temperatures on Earth.

Why is water important?

Water is essential to all animal and plant life on Earth. Plants, for example, use water in photosynthesis to make their food.

Roughly 60% of the adult human body is water and it performs many functions, including:

  • Dissolving vital nutrients in the bloodstream and delivering them to cells.

  • Regulating our body temperature.

  • Dissolving waste substances and carrying them out of the body in urine, faeces and sweat.

  • Protecting tissues, joints and the spinal cord.

Humans need to drink plenty of water to replenish what we lose though sweat, urine, and faeces.

Water quiz

Test your knowledge with this quick quiz.

Where next?

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