Bio-sand filter

Slow sand filtration with a living biological layer at the surface; effective and needs no electricity, but requires a maturation period and careful maintenance.

Cost

Low

Upkeep

Seasonal

Skill to build

Basic

Lifespan

10-20+ years for the tank/media structure; the biological (schmutzdecke) layer needs weeks to re-mature if disturbed, not replaced on a schedule

Embodied carbon

Low

Space / material use

Medium

Output timing

Continuous process

Skill to repair

Basic

Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.

Inputs

• Unheated Water

Outputs

• Potable Water

Sources

• General bio-sand-filter practitioner/NGO durability consensus (CAWST design manuals)

Tutorials

• https://wiki.lowtechlab.org/wiki/Water_-_Biosand_Filter/en
• https://outils-autonomie.fr/filtre-a-eau-a-gravite/

What this page does not tell you

No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.