The Water Cycle

• describe the water cycle

  • EVAPORATION: sun heats Earth's surface -> water -> water vapour
  • TRANSPIRATION: loss of water through plants + leaves
  • +
  • CONDENSATION : moist air rises -> cools + condenses into water droplets -> clouds
  • PRECIPITATION: as water droplets get heavier -> fall as rain/snow/hail
  • PERCOLATION: movement of water intro the ground
• name the changes of state that occur during the water cycle

  • evaporation
  • condensation
• describe the role of plants in this cycle

  • water absorbed from the ground (roots)
  • released into air via transpiration
• whats potable water

  water thats safe to drink
• what do methods on producing potable water depend on

  • available supplies of water + local conditions
• what are the 2 types of water that is used for potable water

  • ground water
  • salty water
• what is groundwater

  • rain provides water with low levels of dissolved substances (fresh water)
  • collects in the ground, lakes + reservoirs
• where is ground water used for obtaining potable water

  • in places where it rains often
  • England
• what is salty water

  • if supplies of fresh water limited due to drought
  • desalination of salty water or seawater required
• where is salty water used for obtaining potable water

  • hot countries
  • Saudi Arabia
• what are the 2 methods of desalination that can be carried out

  • distillation
  • reverse osmosis
• what is reverse osmosis

  • movement of water from low concentration to high concentration
• how does reverse osmosis work

  • pressure applied to salt water
  • so forced through partially permeable membrane
  • from a concentrated -> dilute solution
  • contaminants can't get through
  • fresh water collected
• why is reverse osmosis expensive

  • needs lots of energy for the constant high pressure