The Water Cycle
- Water molecules move between various locations – such as rivers, oceans and the atmosphere – by specific processes
- This is possible because water changes state at a relatively low temperature
The water cycle
- Water enters the atmosphere as water vapour in one of two processes
- Energy from the Sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes
- Transpiration from plants releases water vapour into the air
- The warmer air of the lower atmosphere rises, taking the water vapour with it
- The moist air cools down as it rises
- Water vapour condenses back into liquid water, forming clouds
- Water returns to earth in the form of precipitation
- As the water droplets in the cloud get bigger and heavier, they begin to fall as rain, snow and sleet
- This is called precipitation
The importance of the water cycle
- All life on earth depends upon water for a variety of reasons, this includes photosynthesis
- The water cycle, therefore, is a fundamental process for all living things as it distributes fresh water globally providing us with clean water for drinking
Dealing with drought
- In some areas, drought may become an issue as it means that populations living in those areas would not have access to the potable water they require
- One way to manage this is through desalination of salty water such as sea water
- Desalination means removing the excess mineral ions (salts) from the water to make it drinkable
- There are several ways of removing these salts
- Distillation – saline water is boiled, the water vapour is funnelled through a tube before it is condensed and the pure water is collected
- Reverse osmosis – saline water is forced at high pressure through a partially permeable membrane which filters out all the mineral ions leaving pure water
Reverse osmosis is the most common process used to produce potable water from saline water.
