Maybe the Earth planet should be called Water planet, as a 71% of its surface is occupied by this element.

Water exits on the Earth in three states: solid (ice, snow), liquid and gas (water vapor). Oceans, rivers, clouds and rain are in constant change: the water of the surface is evaporated, the water of the clouds falls, the rain filters by the ground, etc. However, the total quantity of the water in the planet doesn’t change. The circulation and conservation of the water on the Earth is called hydrological cycle or water cycle.

When it was formed, approximately four thousand five hundred millions of years ago, the Earth has already had water vapor in its interior. At the beginning, it was a large ball in constant fusion with hundreds of active volcanos on its surface. The magma, full of gases with water vapor, emerged to the surface due to constant eruptions. Then the Earth cooled, the vapor condensed and fell again on the ground as rain.


The hydrological cycle starts with the water evaporation from the ocean surface. As it elevates, the wet air cools and the vapor transforms into water: it is the condensation. The drops meet and form a cloud. Then they fall by their own weight; it is the precipitation. If in the atmosphere it is too cold, the water falls as snow or hail. If it is warm, it will fall rain drops.

A part of the water that reaches the ground will be used by the living beings; another part will drain in the ground up to reaching a river, a lake or the ocean. This phenomenon is called runoff. Another little of the water will filter through the ground, forming sheets of groundwater. This process is the percolation. Sooner or later, all this water will come back again to the atmosphere, mainly due to the evaporation.

As it evaporates, water leaves behind all the elements which pollute it or which make it not suitable for drinking (mineral salts, chemicals, wastes). That’s why the water cycle gives us a pure element. But there is another process which also purifies the water, and it is part of the cycle: the plant transpiration. The roots of the plants absorb the water, which goes upwards through the stems or logs, taking what the plant needs to nourish. When reaching the leaves and flowers, it evaporates towards the air as water vapor. This phenomenon is the transpiration.

Origin of the water captured for Supply

In Spain, according to the XII National Survey by AEAS published in the year 2012, the superficial origin involves the 83% of the total, while the underground origin involves only the 10%. The rest of it is distributed among the water from the springs (4%) and the obtained in desalination processes (3%).


>>> With the desalination plants which  have been built in the recent years I had the feeling that the percentage of water was bigger. Have you got the same feeling?