water treatment

• where do you get water from (resources)?

  • surface water
  • ground water
  • waste water
• what is surface water?

  • lakes, rivers + reservoirs
  • can dry in summer months
• what is ground water?

  • from aquifers (rocks that trap water underground)
  • in parts of south-east England, 70% and above of domestic water comes from ground water
• what is waste water?

  • water that's been contaminated by human processes
  • e.g as a by-product of industrial processes
• how is water purified in water treatment plants?

  • ground water normally needs less treatment than waste + surface water
  • filtration: a wire mesh screens out large twigs... + gravel + sand beds filter out any other solid bits
  • sedimentation: iron sulfate or aluminium sulfate is added to the water -> makes fine particles clump together and settle at the bottom
  • chlorination: chlorine gas = bubbled through to kill harmful bacteria + other microbes
• how can you get potable water by distilling sea water?

  • sea water can be distilled in dry countries to produce drinking water
  • distillation needs lots of energy so = expensive
  • so don't tend to use in the UK
• why must water used in chemical analysis be pure?

  • deionised water: used in experiments that involve mixing or dissolving something in water
  • so ions cannot interfere with reactions as could give experiment false results
• what is deionised water?

  • water that has had ions (such as calcium + copper ions) that are present in normal tap water removed