Water Treatment (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

• Untreated water contains soluble and insoluble impurities
  • Insoluble impurities include soil, pieces of plants and other organic matter
  • Soluble impurities include dissolved calcium, metallic compounds and inorganic pollutants
• The first step of water treatment is sedimentation / filtration
  • Water is pumped into sedimentation tanks and allowed to stand for a few hours
  • Mud, sand and other particles will fall to the bottom of the tank due to gravity and form a layer of sediment 
  • The water is then filtered through sand and gravel to remove smaller particles 
• The second step is filtration / treatment with carbon (charcoal)
  • This removes unpleasant tastes and odours
• The final step is chlorination
  • Bacteria and other microorganisms are too small to be trapped by the filters 
  • So, chlorine is carefully added to the water supply to kill bacteria and other microorganisms
  • Cholera and typhoid are examples of bacterial diseases which can arise from the consumption of untreated water

Diagram showing the stages in the treatment of water

The stages of treating water are sedimentation, filtration with carbon and chlorination