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?
Constructed wetland / reed bed filtration
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
Land area available for the wetland bed (a real footprint cost), and enough fall from the source to the bed to run on gravity
A bed of gravel planted with reeds, which the used water from sinks and showers flows through. Bacteria living on the gravel and roots feed on the dirt and clean the water as it passes. It needs no power where the ground slopes enough for the water to flow by itself; on flat ground it needs a pump.
15-25 years before media/gravel bed needs partial renewal; the basin structure itself can last far longer
Embodied carbon
Low
Space / material use
High
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.
Constructed wetland / reed bed filtration (This page) 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.
Sand filter 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.
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
Constructed-wetland treatment performance literature (NCBI vertical-flow constructed wetland studies)
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.