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?
Septic tank + drain field
Passive
One of 4 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
Soil percolation rate and area sufficient for a code-compliant drain field; enough fall between tank outlet and field to run on gravity, otherwise a powered lift station is needed
A buried tank where sewage settles and breaks down, with the liquid then soaking into a field of perforated pipes in the garden. Bacteria do the work without air, and the soil finishes cleaning the water. Where the field lies lower than the tank, it runs by gravity with no power at all, so it keeps working in a power cut.
30-50 years for a concrete or fibreglass tank; drain field per the permitted soil/drainage-field figure. Where site levels force a lift-station pump, that pump follows the usual 10-15 year residential pump cycle and becomes the shortest-lived part of the system.
Embodied carbon
Medium
Space / material use
High
Output timing
Continuous process
Skill to repair
Intermediate
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.
Septic tank + drain field (This page) Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you are off the sewer and have a garden for a drain field.
Constructed wetland blackwater treatment Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you want all your wastewater treated on site by planted beds, with no power.
Aerobic treatment unit / micro-station d'epuration (package plant) Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: High · Skill to build: Specialist · Upkeep: Heavy · Change to daily life: Occasional · Works without the grid: No Choose it if your plot is small or wet, where a drain field would fail.
Mains sewer Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Specialist · Upkeep: None · Change to daily life: None · Works without the grid: Yes Choose it if the house is on the public sewer and you want nothing to maintain.
Sources
Septic/wastewater system lifespan industry consensus
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.