Monday, December 24, 2012

How much water is on Earth?

It is estimated that the total amount of water in and on the Earth (including saline and fresh water, liquid and solid water in icecaps, groundwater and surface water) amounts to 1,400 million cubic kilometres –that is, about 332,500,000 cubic miles, which is such a large number that we cannot get a clear picture of it.
This water is distributed as a thin layer with a maximum-low depth of 11,000 metres in the Mariana Trench, the deepest part of the world’s oceans located in the western Pacific Ocean. Taking into account that the Earth radius is more than 6,000 km, this trench is not very deep. Jacques Cousteau, the well-known French oceanographer, used a very graphic explanation to understand how thin this layer of water is: if we immerse a billiard ball into water and then dry it with a towel, the moisture film on the surface of this ball will be proportionally higher than the amount of water on our planet. However, this thin layer takes up 71% of the world’s surface, so most of the Earth is water-covered.
This amount of water has been invariable since it first appeared 4,500 million years ago. Water is neither destroyed nor created, so it will always remain the same. However, what is not the same –be it natural or man made—is the condition and distribution of this water.

How much is drinking water?
Only 2.5% of the planet’s water can be considered fresh water for its low saline contents. Most terrestrial ecosystems and its species (including humans) need fresh water to survive, so even if it is not a scarce resource, it is a limited resource. Out of this 2.5% of fresh water, 79% is found in the icecaps, 20% is groundwater and only 1% is on the surface. Moreover, out of this 1% of surface water, 50% is in lakes, 38% is soil moisture, 8% is in the atmosphere, 1% is found in living beings (like us) and 1% in rivers. In short: accessible drinking water represents only 0.008% of the total available water in our planet. Get this picture to better understand it: if we could include all the Earth water into a 5-litre container, fresh water would be a teaspoonful, but humans could only drink a couple of droplets from it.

  1. These data are taken from the book Guía de bolsillo para personas inquietas:
  2. You can read this book online here:



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