Brief description

Primary use: Producing potable water from contaminated sources.
Secondary uses: Pre-treatment for industrial processes.
Scale: Individual (portable) to municipal (sand beds).

A device or setup used to remove impurities, sediment, and pathogens from water to make it safe for drinking or other uses.

Use / Function

Mechanical Filtration: Layers of different pore sizes trap particles.
- Gravel/Stones: Catch large debris.
- Sand: Catches smaller sediments and organisms.
- Cloth/Ceramic: Catches very fine particles.
Adsorption: Charcoal (activated carbon) absorbs chemicals, odors, and toxins.
Biological Action: In slow sand filters, a “schmutzdecke” (biological layer) forms on top, where microorganisms consume pathogens.

Bio-Sand Filter (Household):

Container: Use a tall barrel or bucket with a tap at the bottom.
Drainage Layer: Place a layer of clean gravel at the bottom to cover the outlet.
Separation: Place a mesh or fabric over the gravel to prevent mixing.
Filtration Layer: Fill the bulk of the container with fine, washed sand.
Adsorption Layer (Optional): Add a layer of crushed charcoal for chemical purification.
Operation: Pour water slowly. The first few liters should be discarded until the water runs clear.

Ceramic Filter: Porous clay pot impregnated with silver (antibacterial). Very effective against bacteria.
Cloth Filter: Folded sari cloth (used in Bangladesh) filters out copepods that carry cholera.
Solar Disinfection (SODIS): Using clear bottles and sunlight (UV) after filtration to kill remaining viruses.

Viruses: Basic sand filters may not remove all viruses (too small). Boiling or chemical disinfection is still recommended.
Maintenance: Filters clog over time and need cleaning (backwashing) or replacing.
Breakthrough: If flow is too fast, contaminants can be pushed through.
Chemicals: Standard filters don’t remove dissolved heavy metals or salt.