Water Purification Plant. Image credit cdrmaguire.com

Water Purification Plant. Image credit cdrmaguire.com

ZIMSEC O Level Combined Science Notes: The purification of Water

  • Large residential areas such as Harare, Chitungwiza and other urban establishments are supplied with piped running water
  • This water is treated so that it is safe to drink and for other domestic use
Water purification process

Water purification process

  • The water is usually obtained from a dam, reservoir, lake or river
  • It is then passed through a purification plant before it is piped for domestic and industrial use
  • The purification plant uses chemical and physical process to make sure the water is safe and clean
  • First the water is allowed to settle so as to remove solid particles which fall to the bottom
  • The solid matter is then removed
  • A chemical called a flocculant is usually added to speed up this sedimentation process
  • The water is then filtered through sand to remove any remaining solid particles
  • The water will now be clean but not yet safe to drink
  • The water is then chlorinated 
  • Chlorine is added to kill any pathogens, bacteria and any other undesirable micro-organisms
  • At this stage the water is then safe to drink
  • It is then passed into a storage reservoir until it is pumped to houses
  • The water is constantly tested  for bacteria at various stages to make sure it is safe to drink

Domestic filters

Home built filter

Home built filter

  • Domestic filters are used in some homes to make water safe to drink when it is obtained from an unsafe source such as a river
  • They make use of sand particles of different sizes
  • With time the sand becomes compacted and microorganisms grow within the filter helping to make it more effective
  • The sand in this domestic  filters has to be replaced from time to time

To access more topics go to the Combined Science Notes page.


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