Water (H2O) is a chemical compound of hydrogen and oxygen. It is the only chemical compound on earth that occurs naturally in all three states of matter.
The term water usually refers to the liquid state. In the solid state it is called ice and in the gaseous state it is called water vapour.
Water is the basis of life on earth and also the basis for diving itself.
Basic knowledge for Open Water Diver* (OWD*)
Water covers almost 71% of the earth's surface. It forms the basis for all known life on planet earth. Even the human body consists of 50% to 75% of water.
In its pure form, water hardly ever occurs in nature, but always contains dissolved gases and salts. If the salt content is below 0.1%, this is called fresh water. Its density is almost exactly 1 kg per liter.
The salt water of the seas and oceans contains an average mass fraction of 3.5% of dissolved salts. Salt water therefore has a higher density than fresh water, which leads to a greater buoyancy and consequently to the fact that one has to carry more lead weights in the sea with the same equipment configuration to compensate.