household water treatment and storage methods

steps

  1. pre-treatment
  2. filtration
  3. disinfection
  4. safe storage

metrics

  • effectiveness

  • efficiency

  • different methods have their own advantages and disadvantages

pretreatment

  • removes any suspended solids, turbidity

rough filtration

  • cloth and sand filtration
  • sedimentation
    • passive:
      • letting water sit still overnight
    • assisted:
      • using coagulant like alum

advantages

  • filters remove large pathogens like guinea worms and protozoa
  • sometimes work for bacteria and viruses
    • but only if designed so
    • not the norm
  • filtration is popular with people since the process is very visual
    • dirty water goes in and clean water comes out
    • and residual is collected
    • easy for people to understand
  • filtration doesn’t impart a strange taste to water
  • ceramic filtration can even cool the water
  • turbidity caused by high iron and similar particles is removed

disadvantages

  • need for supply chains
  • replacing broken components
  • recontamination of filtered water during transportation

disinfection

boiling

  • everyone around the world understand that boiling purifies water

  • highly effective against all classes of pathogens

  • when biomass fuel is used for boiling, it causes health risks
  • boiling needs fire
    • fire == indoor air pollution
    • fire == fuel == money
    • boiling is an expensive part of water treatment

drawbacks

  • boiled water has a flat taste,
  • sometimes chalky precipitates, formed during boiling
    • doesn’t look nice
  • vulnerable to re-contamination
  • boiled water has to be cooled before drinking
    • risk of recontamination if done in an open container

UV radiation (SODIS)

  • ultraviolet lamps are used
  • UV rays of the sun can be used
    • SODIS: solar disinfection
  • different pathogens tolerate UV to various extents
    • bacteria such as e.coli are quickly killed
    • crytoptosporodoum is somewhat more tolerant to heat
    • some viruses can withstand the high UV doses
  • treatment done in the storage container
    • recontamination opportunities are low

SODIS drawbacks

  • time consuming, only small amounts of water treated at a time
  • water has to be cooled overnight to be consumable
  • does not work if turbidity shields pathogens
    • water has to be pretreated well

Chlorine

  • chlorine can be applied in liquid or tablet form
  • more effective with longer contact times
    • usually should be given 30 minutes to disinfect water
  • chlorine is inexpensive and can be applied at household levels easily
    • large volumes can be treated in short periods of time
  • residual chlorine can protect against recontamination

drawbacks

  • more effective against bacteria
  • high doses needed to kill viruses
  • some protozoan cysts are highly resistant to chlorine
  • cryptosporodium cysts can survive full strength undiluted bleach for short periods

  • less effective on turbid water

  • consistent chlorination requires supply chains and ongoing commitment from users
  • chlorine have a distinctive taste and odor if people are not used to it