The water is an important substance on Earth with many physical and chemical properties, the basis condition of life.
Earth is covered 70 % by water. There is water not only in seas, lakes, rivers, snow-fields, but in the air (steam, water drops) and in the ground there is also water. The hydrosphere - which contains natural water in different physical states - is blending with the atmosphere 10 km in  the  heigh and also with the  solid stratum 5 km in the deep. The water stock is practically constant on Earth, approximately 1,4 thousand million km3:  97,3 % salted water and  2,7 % sweet water.
The attributes of water can be examinated from the geographical, biological, physical or chemical points  of view. In what follows we will discuss the chemistry of water and some chemical methods - especially  the rapid tests.

        The imptance of water