Water Treatment (Cambridge International IGCSE Science)

Spec point — Describe the treatment of the domestic water supply in terms of: sedimentation and filtration to remove solids use of carbon to remove tastes and odours chlorination to kill microbes (pathogens)

Water treatment

• 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

1. The first step of water treatment is sedimentation and filtration to remove solids

• 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

1. The second step is filtration through carbon(charcoal)

• This removes unpleasant tastes and odours

1. 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 microbes
• 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

Exam Hint Exam questions on water treatment often focus on the purpose of each stage of the process.