Water

The physical properties of water

Water has a high specific heat, i.e. it needs a lot of heat to heat up and takes long to lose the stored heat and get cold. This is why it is used in cooling systems (for instance in car radiators or to cool industrial equipment). And this is also why in coastal (or lake) regions the temperature of the air is milder: in these areas, as seasons change, the temperature of the water ‘mitigates’ the temperature of the air, since it decreases or increases more slowly than that of the air. Water has a high surface tension: that means that, once poured on a smooth surface, it tends to form spherical drops instead of expanding into a thin film. Without gravity, a drop of water would be perfectly spherical. Surface tension allows plants to absorb the water contained in the soil through their roots. And it is surface tension, again, that makes blood, which is largely composed of water molecules, flow through the blood system of our body.
Only liquid water?
In addition, water can normally be found in a liquid state, but can easily become solid or gaseous. Pure water goes from liquid to solid, i.e. freezes, at 0 degrees centigrade, while at sea level it boils at 100°C (the higher the level, the lower the temperature at which water starts boiling). The water boiling and freezing values are taken as a reference point to calibrate thermometers: in centigrade scales, 0° on the centigrade scale is the freezing point and 100° is the boiling point.
When freezing, water expands, i.e. its density decreases while its volume remains the same: this is why ice floats on the water or a bottle filled with water and placed in a freezer breaks up.
Water is a special natural resource since it is the only one on earth to be found in all of the three physical states depending on the surrounding temperature: liquid, solid (ice) and gaseous (water vapour).
The whole of the processes that make water leave the oceans, get into the atmosphere, reach the emerged lands and flow back to the oceans later on is called hydrological cycle  and is fuelled by the energy of the Sun.