Technology

There are three primary methods of filtering water to make it potable, BioSand Filter, Safe Water System, and PuR. Read on to learn about each.

BioSand Filter

The filter is a concrete container, enclosing layers of sand and gravel whose purpose is to eliminate sediments, pathogens and other impurities from the water. Water is poured into the top of the filter as needed, where a diffuser plate placed above the sand bed dissipates the initial force of the water. Traveling slowly through the sand bed, the water then passes through several layers of gravel and collects in a pipe at the base of the filter. At this point, the water is propelled through plastic piping encased in the concrete exterior, and out of the filter, for the user to collect.

Advantages

  • Effective against bacteria, viruses, and parasites
  • Removes turbidity
  • Quality of water improves with time
  • High flow rate - 60 liters/hour
  • No on-going costs - no replaceable parts
  • Durable & robust- lasts at least 5 years
  • Fabricated from local materials
  • Water tastes & looks good

Constraints

  • Heavy - difficult to move
  • Biological layer takes 1-2 weeks to develop to maturity
  • Must be maintained, especially in situations where water is very muddy
  • Requires that someone conduct maintenance checks by going from house to house
  • Requires that the filter be used periodically on a regular basis

Additional Resources

Safe Water System (SWS)

Chlorine disinfection is accomplished by adding chlorine into the water. Users add one cap of solution to their storage container. Chlorine disinfection reduces diarrhea by 22-84% (CDC 2005). By providing sufficient contact time with the water, the chlorine causes chemical reactions which change the contaminants in the water, inactivating or killing them. It also causes chemical reactions which inactivate organic matter.

Advantages

  • Kills bacteria and viruses effectively
  • Residual chlorine protects water for a period of time
  • Extensively field tested
  • Easy to use

Constraints

  • Requires clear water to be most effective
  • May not be effective at killing parasites
  • Taste unacceptable to some
  • Contact time for chlorine to sit in water required
  • Chemical dosage required varies with water quality

Additional Resources

PuR

PuR is a Point-of-Use (POU) water treatment product sold in powder form by Population Services International (PSI). One packet of powder is added to 10 L of water. Users stir, let the solids settle, strain the water through a cloth, and wait 20 minutes. PuR reduces diarrhea by 16-90% (CDC 2005). PuR inactivates pathogens like chlorine disinfection, but an added chemical allows it to make the solids in the water drop out.

Advantages

  • High drinking water quality – drinking water is visibly clean
  • Effective even in turbid or muddy waters
  • Kills bacteria, viruses, and parasites effectively
  • Residual chlorine protects water for a period of time

Constraints

  • Requires multiple steps for correct use
  • Users must have two buckets, cloth, and stirring device
  • May be too expensive for some
  • Contact time for chlorine to sit in water required

Additional Resources