The main feature of the water on Earth is its flux, which is a consequence of the warmth effects of sun and thermal dynamics of the atmosphere. The water constantly circulates in nature between the Earth and the atmosphere. This flux of water is called hydrological cycle. The water constantly circulates between air, water and land masses. Under the influence of solar energy every day it evaporates a large amount most of which returns to the lakes, seas and oceans, and a smaller part as maturities are distributed on the mainland, powering sources and lakes which make life possible. The water consumed and circulated on Earth is a hundred million years.

 Water moves, changes shape, is consumed by plants and animals, but never disappears for us permanently. The circular process of water appears in five processes: condensation, precipitation, infiltration, leakage and evaporation or transpiration. These five processes together make up the hydrological cycle.

Water is valuable as a solvent for organic and inorganic materials and products of metabolism through it that forms the basis of life on earth. Water molecules participate in important physiological processes, the process of photosynthesis, water is a hydrogen donor, the cell breathing is one of the final products. Water facilitates colidal state of protoplasm, as aka is necessary for thermo regulation of living cells. It is necessary to maintain the unity of the structure of the cell, tissue and the whole organism.

Water is a prerequisite for life and represents:

• natural wealth
• a basic condition for the existence of life and the environment from which it originated
• substance that is necessary to complete biocoenosis including humans, irreplaceable material
• source of food and minerals
• environment for many life processes
• natural aesthetic element
• environment for recreation.