Sources of Fresh Water (Cambridge International IGCSE Environmental Management)

What are the main sources of fresh water?

• Fresh water refers to water with low salt content, used by people for drinking, washing, farming and industry

  • Only a small percentage of Earth’s water is fresh water

Sources of fresh water

• People obtain fresh water from four main sources:

  • Atmosphere
  • Surface water
  • Groundwater
  • Desalinated ocean water

Atmosphere: rain and snow

• Rain and snow come from precipitation, when water vapour in the atmosphere cools and falls to the Earth

  • Used directly by plants and stored in rivers, lakes and groundwater

• Many regions depend on seasonal rainfall for drinking water, farming and filling reservoirs

• Snow in mountains melts in warmer seasons

  • Meltwater feeds rivers and provides water during dry periods

Surface water: rivers, lakes and reservoirs

• Surface water is fresh water found above ground

Rivers

• Flow across the land and collect rainfall and meltwater

  • Used for drinking water, irrigation and hydroelectric power

Lakes

• Store large amounts of water in natural basins

  • Provide a reliable supply throughout the year

Reservoirs

• Reservoirs—artificial lakes created by building dams

  • Store water for cities, agriculture and industry
  • Help control flooding and maintain water supply during droughts

Groundwater: aquifers and wells

• Groundwater is stored below the Earth’s surface in soil and rock

Aquifers

• Aquifers—underground layers of rock that hold water

  • Filled by rainwater soaking into the ground

• Provide clean, filtered water for drinking but hard to access

Wells

• Wells are holes dug or drilled into the ground to reach aquifers

  • Communities pump water to the surface for home use, farming and livestock

Oceans: desalination plants

• Oceans contain salt water, which is not safe to drink

• Desalination is the process of removing salt from seawater to make fresh water

  • This can be done using heat (distillation) or membranes (reverse osmosis)

• A desalination plant is a large facility where machines remove salt from seawater to produce fresh drinking water

• They are usually found in coastal areas where freshwater supplies are limited

• They are useful in dry countries with little rainfall

  • Provides a reliable supply but uses large amounts of energy

Desalination process

Exam Hint You need to be able to describe how desalination plants actually work (i.e. how they use distillation or reverse osmosis) to turn seawater into fresh water. This is covered in detail in our revision note page on desalination.