Water is present on earth in various forms: in solid form (snow and ice), in fluid form (water) and in gaseous form (water vapour). These situations always merge into each other. This constant transition from the state of the water is called the ‘cycle of the water’. In the drawing below, the cycle of the water is shown.

Figure 1: The large cycle

The heat from the sun causes the water to evaporate. This evaporated water rises up as water vapour. This happens mainly above sea, because most of the earth’s surface consists of sea.

The water vapour produces clouds. As the clouds cool down, they can’t hold the water. Depending on the temperature, it starts to rain, snow or hail. This happens, for example, when clouds are driven over land, where the temperature is lower or when clouds have to rise against a mountain range.

The rain sinks into the ground and flows back to the sea under the ground. Sometimes the water breaks out of the soil and continues its way to the sea along the surface: through springs, streams and rivers.

Snow falling high into the mountains forms glaciers there. The glaciers are slowly descending. They melt at the bottom and the water then flows in the direction of the sea.

There is a difference between the large cycle (described and illustrated above) and the small cycle.

The small cycle does not start above the sea, but above the inland waters (see the picture below). This cycle therefore takes place in a smaller area, for example within a country or region.

Figure 2: The small cycle