Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?

Bio-sand filter

Passive

One of 5 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.

A tall container filled with layers of sand and gravel that water is poured into and slowly passes through. A living layer of tiny organisms grows on top of the sand and eats germs, while the sand holds back dirt. It makes water safe to drink with no electricity, but takes time to start working and needs regular care. The proven design, rated here, is a concrete body about a metre tall; a small version in a plastic pipe gives about 5 litres a day, but its water had not been tested safe when it was published.

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

Inputs

• Unheated water

Outputs

• Potable water

Compare the 5 ways to meet this need

Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.

• Bio-sand filter (This page)
  Can I use it? Works in a flat · No rebuilding needed
  What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Regular · Change to daily life: Daily · Works without the grid: Yes
  Choose it if you want safe drinking water with no electricity, from a filter you can build.
• Multi-stage filtration + UV disinfection
  Can I use it? Works in a flat · No rebuilding needed
  What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Heavy · Change to daily life: None · Works without the grid: No
  Choose it if you want the whole house on safe drinking water from rain or raw water.
• Ceramic candle filter (silver-impregnated)
  Can I use it? Works in a flat · No rebuilding needed
  What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Regular · Change to daily life: Daily · Works without the grid: Yes
  Choose it if you want drinking water with no power from a pot on the counter, with nothing to build.
• Reverse osmosis (RO) filtration
  Can I use it? Works in a flat · No rebuilding needed
  What does it cost me? Upfront cost: High · Skill to build: Specialist · Upkeep: Heavy · Change to daily life: None · Works without the grid: No
  Choose it if your water carries nitrates, metals or salts and you want the purest drinking water.
• Solar still (solar distillation)
  Can I use it? Works in a flat · No rebuilding needed
  What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Daily · Works without the grid: Yes
  Choose it if your only source is salty or badly polluted and you have sun.

Sources

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

Limitations of this page

We don’t list sizing or quantities, as the yield of each technique depends on the quality of its build. The catalogue compares options but doesn’t dimension them. Regulatory notes are indicative, with a French example, and need to be confirmed locally.