The global water cycle

• Aquifers most commonly form in rocks such as chalk and sandstone, which are porous and permeable
• Just over 30 per cent of all freshwater is stored in rocks deep below the ground surface forming vast underground reservoirs called aquifers
• The distribution of land, sea, and ice sheets has a profound impact on the global distribution of water
• Aquifers can be depleted unsustainably as they exist where seawater has intruded due to over-abstraction
• The upper level aquifer is called the water table. This rises and falls with the seasons, with water abstraction (additional water taken out) and recharge (water added back in). With good management, the water table can be kept at the same level - sustainable abstraction
• Types of aquifers

  • North-west Sahara aquifer system
  • High Plains aquifer
  • Guarani aquifer
• Important facts about water storage

  • The vast majority of the Earth's water is saline water
  • Only 2.5 per cent of the Earth's water is freshwater.
  • Almost all of which is stored as snow and ice (68.7 per cent) and groundwater (30.1 per cent).
  • Surface and other freshwater comprises only 1.2 per cent of all freshwater
• Water is stored within four major physical systems

  Lithosphere (land), hydrosphere (liquid water), cryosphere (frozen water - snow and ice) and atmosphere (air)