Water Cycle 1.1

Learning Intentions and Overview

  • Learning Intentions:

    • Understand the steps involved in the water cycle and how water is recycled.

    • Describe the processes involved: evaporation, condensation, precipitation.

    • Make a model of the water cycle and show the steps that occur in the cycle.

The Water Cycle Summary

  • The water cycle describes the movement of water in, on and above the surface of the Earth.

  • Water enters the atmosphere due to evaporation from lakes and the sea; industry; through plants during transpiration; and the burning of most fuels.

  • Water is removed from the atmosphere by precipitation, including rain, hail, sleet and snow.

Materials: States of Matter

  • Water can exist in a number of states:

    • Solid (ICE)

    • Liquid (WATER)

    • Gas (STEAM)

Definitions of Key Processes

  • Evaporation: The changing of liquid to a gas at the surface of the liquid.

  • Condensation: Changing of a gas to a liquid.

  • Precipitation: Precipitation is any product of the condensation of atmospheric water vapour that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow and hail.

  • Transpiration: Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99.5%97\text{--}99.5\% is lost by transpiration.

Steps in the Water Cycle

  1. Heat from the Sun: Heat from the Sun causes water to evaporate from the oceans.

  2. Cooling and Condensation: As water vapour rises, it cools. Condensation produces clouds of tiny droplets of water.

  3. Precipitation: Clouds rise and further cooling occurs. Drops of water become heavier and fall as rain. Clouds blown by wind.

  4. Collection: Water collects in streams and rivers.

  5. Flow to Sea: Rivers flow to the sea; they dissolve substances from the rocks and receive sewage and industrial waste.

  6. Reservoir Diversion: Some water is diverted to reservoirs.

  7. Purification: This water is purified in the water treatment works.

  8. Usage: It is then used in homes and industry.

  9. Treatment: After use it is treated in sewage works.

  10. Return: It is then returned to the rivers and the sea.

  • Transpiration: Plants lose water through leaves.

Importance of the Water Cycle

  • Water plays a very important part in our lives.

  • Our bodies are made up of about 70%70\% water.

  • Approximately 80%80\% of the Earth’s surface is covered in water.

  • Water is continually moving from the Earth’s surface to the clouds and then back to the Earth again as rain and snow.

  • This affects our climate.

  • This in turn affects the habitats on which many plants and animals depend.

Benefits of the Water Cycle

  1. Without the water cycle the world would be a desert. We would have to irrigate the land in order for it to be useful to grow crops and feed livestock. This would be very expensive.

  2. We would have no fresh water to drink from the tap. Water that has evaporated is clean and free of salts. We would have to desalinate water (remove salts) and this would be very expensive.


  • Research Task: How does climate change affect the water cycle? Research this and make notes in your copy.