Importance to life

Nearly all substances become heavier and thicker when converted from a liquid to a solid state. Water, however, increases in volume and becomes lighter when it turns into ice. This property is of vital importance for sustaining life in basins during winter.

A drop of rainwater falling through the air dissolves atmospheric gases. When rain reaches the Earth, it affects the quality of the land, lakes and rivers.

Water can store huge quantities of energy, which can turn oceans, seas and lakes into giant heat reservoirs. This particular property influences climates in areas situated near water basins. It is also due to its energy-retaining quality that water is widely used for cooling and transferring heat in thermal and chemical processes.

Water-surface tension is a measure of its surface-film strength. The attraction between water molecules creates a strong film, which among other liquids is surpassed only by mercury. This surface tension permits water to hold up substances heavier and denser than itself. Some aquatic insects, such as the water spider, rely on surface tension to walk on water.

Water surface tension is essential for the transfer of energy from wind that creates waves. Waves are necessary for rapid oxygen diffusion in lakes and seas.

In a thin glass capillary, for example, when molecules at the edge reach for and adhere to the molecules of glass just above them, they tow other water molecules at the same time. The water surface, in turn, pulls the entire body of water upward until the downward force of gravity is too great to be overcome. This process is called "capillary action," and it allows a sponge to be used to soak up spilled water. Without this property, the nutrients needed by plants and trees would remain in the soil.

A large percentage of our blood is water. People must exchange about two litres of water per day in order to regulate their body temperature.

Places where water is preserved on land are called water basins. Water can be found in rivers, lakes, pools, animals, plant stems and under the ground.