The natural water cycle is the continuous movement of water between the land, the ocean, rivers and creeks, and the atmosphere.
Water is always cycling around, through, and above the Earth. As it moves through the cycle, water continually changes from liquid (rainwater, saltwater) to gas (water vapour) and back to liquid. The liquid can also get cold and become solid (ice or snow).
The water cycle is essential for the survival of life on Earth. It has been happening for billions of years. In fact, the water that we drink today could have been drunk by a dinosaur, millions of years ago. The good news is that the water has been cleaned many times since then, as the Earth's fresh water supplies are constantly refreshed through the natural process we call the water cycle - our planet's way of recycling water.
When the sun shines on oceans, rivers, creeks and other water bodies, it causes water (in liquid form) to evaporate.
The heat from the sun provides enough energy for the hydrogen bonds between water molecules to break and the individual water molecules to drift upwards to the atmosphere as water vapour (in gas form).
When the water in the ocean evaporates, salt, minerals and metals are left behind which means that only fresh water makes its way up to the clouds.
Evaporation is the process that describes water changing from a liquid to a gas.
As the water vapour rises, the air becomes cooler and the water vapour condenses back into liquid water droplets. The water droplets merge together to form clouds.
Condensation is the process that describes water changing from a gas to a liquid.
When the conditions are just right the water droplets fall back down to Earth as precipitation. Depending on the air temperature, the water droplets can return to the Earth in either a liquid form (as rain) or in a solid form (as snow, sleet or hail).
Precipitation is rain, snow, sleet or hail falling from the sky.
When the water returns to Earth, it either infiltrates the surface and collects underground in aquifers or becomes run-off that flows into rivers and streams.
Infiltration occurs when water falls and soaks into the ground.
Run-off is when water does not soak into the ground and flows into streams and rivers.
Water that infiltrates the Earth's surface can also be absorbed by the roots of plants. This water travels up through the plant to the leaves, where some of it is used in the process of photosynthesis. On a warm sunny day some of this water is lost through the leaves. This process is referred to as transpiration.
Transpiration is the evaporation of water from plants.
As the water moves from liquid to gas and back to liquid before returning to earth, this natural process removes some of the impurities in the water.