# Water on Earth

The total amount of of water on Earth is about 1420 000 000 km3. Evaporation from the surface of the Earth amounts to about 291 200 km3, runoff to the sea to about 32 760 km3 and rain about 87 360 km3 per year.

The total amount of Water on Earth (Source: Cooks)

A large amount of water is stored in people, animals and plants. Calculate the amount of water stored in the world’s human population by using the following data:

People: 6000 000 000 (6 thousand million)
Body water (approximately): 75% (per person)
Body mass (average): 60kg (per person)

Use the following formula to get the answer:

(60 x 75)/100 x 6000 000 000 litres = ?......... Megalitres (1 Megalitre = 1 million litres).

Compare this figure with the capacities of:

the Vaal Dam: 2 570 000 Megalitres
the Katse Dam: 1 950 000 Megalitres
the Grootdraai Dam: 350 000 Megalitres

##### Note: An even greater volume of water is stored in plants and animals worldwide!!

Water is a transport medium as it carries along many substances from one place to another, just like a train. Water is made up of molecules, and each molecule contains 2 hydrogen atoms and 1 oxygen atom. This is shown in its chemical formula H2O. When a lot of these H2O molecules join together, they form water. When water falls on the Earth’s surface from the clouds in the form of rain, it picks up a lot of substances which are then transported in the water, e.g. silt particles, organic material like leaves and branches, bacteria, etc., just like a train picking up passengers. Water is the train that moves along its tracks, and the passengers are the substances that are carried along on the train.

## Also see:

Types of Water
Water as a Force in Nature
Sources of Water