The hydrological cycle is the continuous movement of water between the earth and the atmosphere. Water evaporates from water and land surfaces and transpires from living cells. This vapour circulates through the atmosphere, condensing to form clouds and precipitating as rain or snow. When water hits the earth's surface it either runs into streams and ends up in oceans or lakes, or seeps into the soil. The water that seeps into the soil is then either absorbed by the roots of vegetation, or it sinks into the groundwater reservoir.
Water is made up of hydrogen and oxygen.
Two hydrogen atoms are linked by a single chemical bond to one oxygen atom. The water molecule is angular in shape, forming negative and positive charges on opposite sides. This means that the H 2 O molecule is highly polar. These strong hydrogen bonds mean that water has a very high boiling point because it takes a lot more energy to overcome them and release H 2 O molecules from the liquid into the gaseous phase. The H 2 O molecules in ice are highly ordered, although loosely structured.