Water is less dense in its solid state than in its liquid state, so that ice floats instead of sinking. This property permits life to develop in polar and subpolar regions where ice floats and allows life to continue living below the surface. If ice were heavier than water, it would sink, and more ice would form on top of it. As a result, all life in the waters would be trapped in the ice in the many areas of the world where it gets cold enough to freeze water.

Water is a remarkable solvent, where most elements and compounds can dissolve in its powerful molecular structure. Gases such as oxygen and carbon dioxide, can also dissolve, making it readily available for photosynthetic and nonphotosynthetic organisms to use.