Water Treatment (CIE IGCSE Chemistry)

Water supply

• Water is taken from rivers, reservoirs or underground water sources (groundwater)
• A rock that stores water is known as an aquifer

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
• Water is pumped into sedimentation tanks where the water is 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, in a process called sedimentation
• Filtration is the process used to remove smaller particles by passing the water through layers of sand and gravel filters that trap solid particles
• Water can also be passed through carbon (in the form of charcoal) to remove tastes and odours
• Bacteria and other microorganisms are too small to be trapped by the filters so chlorination is used
• This involves the careful addition of chlorine to the water supply which kills bacteria and other unwanted 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