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Bio Sand Filter

Dilemma in Medical Missions

When many short term mission teams visit the field, they find people suffering from parasitic infections, and they hand over some pills, hoping to heal them. But they eventually have to depart from the field, knowing that simply ingesting the pills a few different times will not solve the main problem. Then, how can we help to prevent the natives from parasitic infection?

Answer: Bio Sand Filter (BSF)

The solution is for them to drink clean and safe water, not contaminated with parasites. SWIM seeks to deliver clean water to many nations, so we build low-cost and semi-permanent bio sand filters in mission field, and we also train the native there to build them with parts easily found there. We aim to improve their hygiene by using and building BSF on their own.

And the issue of water contamination is not restricted to parasites only. According to WHO's statistics, 85% of all the world's diseases stem from using dirty and contaminated water. In other words, if they could simply have access to clean and safe water, many of people in third world country can be freed from such diseases. BSF is a life-giving device for many of them.

Pathology of Waterborne Diseases
  • Excrements-Mouth:  Diarrhea, Cholera, Parasite (Helminth), Typhoid Fever

  • Water Washed: Trachoma, Skin Infections

  • Water Based: Schistosomiasis, Guinea Worm (A tapeworm from India and Africa that resides under animal or human skin)

  • Insects-Pests: Mosquitos - Malaria, Dengue Fever, Tsetse Fly (A housefly in Central-southern Africa that causes sleep disease)

Three-Step Water Filtration
  1. Sedimentation

  2. Sand Filter

  3. Disinfection

Biosand Filter Mechanism
  • Separation: Parasites, insects, and sediment are stuck within sand particles.

  • Absorption: Virus are absorbed through sand particles and do not travel through.

    • A virus that is once absorbed is deactivated through antibiotics.

  • Predation: Microorganism layer kills off bacteria and pathogen within the water.

  • Natural Death: Pathogens that do not receive enough oxygen or nutrients in water will die naturally.

Removes most water pathogens
  • Parasites: 100%

  • E.Coli: 98%

  • Virus: 95%

  • Turbidity: 95%

  • Iron: 90%

  • Arsenic: 95% (also through hypochlorite & ferric sulphate treatment)

Pros / Cons of Biosand Filter


  • Removes up to 98% of bacteria and 100% of parasite, as well as particular iron and manganese.

  • Building materials can be obtained anywhere, and can be built at a low cost ($15-$40)

  • There is no upkeep cost ($5/year) and is durable enough to be used for many years.

  • Has a great water taste, and can be used as a business item.


  • Cannot remove coloring or soluble substances (sodium, pesticides, chemical fertilizer, heavy metals)

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"and what you have heard from me in the presence of many witnesses entrust to faithful men, who will be able to teach others also."

2 Timothy 2:2 (ESV)

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