The water cycle

The water cycle refers to the continuous flow of water on our planet, at ground level, above ground level and below ground level. This process helps to keep vegetation hydrated, to renew the water in oceans, seas and waterways and it makes it rain too.

So what happens before it rains? First, the energy from the Sun heats the surface of the Earth; water from oceans, seas and other waterways evaporates; this warm moist air from the evaporation process goes up; the water vapour then becomes water droplets again in the condensation process and we get clouds; the water droplets then become big and heavy and begin to fall out of the sky as rain drops. Other weather conditions and temperatures influence the kind of precipitation: it can be rain, snow or sleet.

Some of that precipitation goes on people's head or umbrella, but what happens to the water then? Well, an impermeable surface like a pavement or road means we have surface run-off and the water goes back into the cycle. In woods or fields, for example, there is through flow and the water infiltrates the ground. Some water goes deep underground. This water percolates the ground and re-enters the cycle via a river or sea.

The water cycle is constant because we have enormous stores of water in the ocean, ice-cap, land and the atmosphere.