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?
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.
What your site needs
Enough fall from the source through the filter bed to run on gravity, otherwise a feed pump
A tank or bed of sand that used water trickles down through. The sand holds back particles and the life that grows in it cleans the water further, either on its own or before a reed bed. It needs no power where the ground slopes enough for the water to flow by itself; on flat ground it needs a pump.
10-20 years before media needs replacement (depends heavily on loading and pre-filtration upstream)
Embodied carbon
Low
Space / material use
Medium
Output timing
Continuous process
Skill to repair
Basic
Regulation (FR example)
On-site sanitation (assainissement non collectif): the installation must be declared to and approved by the local SPANC before work starts, and is subject to periodic inspection. Arrete du 7 septembre 2009 modifie.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
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: None · Works without the grid: Yes Choose it if you want a compact filter for greywater, on its own or ahead of a reed bed.
Constructed wetland / reed bed filtration Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: Light · Change to daily life: None · Works without the grid: Yes Choose it if you have room and a slope, and want greywater cleaned by plants with no power.
Greywater heat recovery (drain water heat exchanger) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: None · Works without the grid: Yes Choose it if you want to get back the heat of shower water, with nothing to switch on.
Membrane bioreactor (MBR) greywater recycling package unit 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 you want greywater clean enough to flush toilets indoors.
Wood-chip filter (Filtres a Broyat de Bois, FBB) Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Regular · Change to daily life: None · Works without the grid: Yes Choose it if you want the simplest greywater filter to build, topped up with wood chips.
Sources
Water filtration component lifespan industry sources (CleanWaterStore; SimplePure RO guide; ESP Water Products UV guide)
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.