How Biosand Filters Work

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How Biosand Filters Work

Simple Design. Powerful Results.

Biosand filters are a proven, low-maintenance technology that transforms unsafe water into clean, drinkable life — without the need for electricity, chemicals, or complex parts.

Each one is handcrafted by skilled teams in Cambodia using local materials, and built to last for over a decade. 

Here’s how they work:

The Structure

  • Size: Roughly 3 feet tall and 30cm x 30cm wide
  • Materials: Concrete body filled with layers of fine sand and gravel
  • Flow Type: Gravity-fed — no electricity or plumbing required
  • Output: Clean, safe drinking water in minutes

The Filtration Process

  • 1. Source water is poured into the top of the unit.
  • 2. A diffuser plate gently distributes water, preventing disturbance of the filter surface.
  • 3. Water passes through a biological layer (called the schmutzdecke) — a living micro-layer that forms naturally on the surface of the sand and consumes harmful bacteria.
  • 4. It continues downward through fine sand, which traps parasites, protozoa, and organic contaminants through physical and chemical processes (like adsorption).
  • 5. Water then flows through coarse gravel layers that support drainage and prevent clogging.
  • 6. Finally, clean water exits through a spout — ready to drink.

What It Removes

Extensive research by the Center for Affordable Water and Sanitation Technology (CAWST) shows biosand filters remove:

  • Up to 99.9% of protozoa (Giardia, Cryptosporidium)
  • Up to 98.5% of bacteria (including E. coli)
  • Up to 95% of turbidity (cloudiness from particles)
  • Up to 90–95% of iron (common in well and surface water)

These numbers may vary slightly based on usage and water quality — but the results speak for themselves. With proper use, biosand filters produce safe drinking water for 5–8 people for 10+ years.

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Maintenance and Training

The filters require minimal upkeep:

  • Occasional stirring and removal of surface sediment
  • No moving parts to break
  • No replacement cartridges required

Families receive basic hygiene training and a demonstration of how to use and maintain the filter. Our local teams provide support as needed to ensure every filter remains effective long term.

Sustainable by Design

  • Made entirely with local materials — supporting local jobs
  • No external energy needed — perfect for remote villages
  • Long lifespan — up to a decade or more of protection

This is one of the most sustainable water solutions in the world. Low cost. Low tech. Life-changing.

Read the Cambodia Project
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