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?
Direct greywater diversion to toilet flushing
Passive
One of 2 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
Shower or bath water diverted straight to the toilet cistern or bowl by gravity or a simple bucket, with no treatment beyond settling, the lowest-tech greywater reuse there is. Same-day use only, since untreated greywater develops odor and bacterial growth within hours to a day or two of storage.
Matches plumbing/diversion-valve lifespan, 20-30 years for simple gravity diversion hardware
Embodied carbon
Low
Space / material use
Low
Output timing
On-demand/controllable
Skill to repair
None
Regulation (FR example)
Greywater reuse is permitted under decret 2024-796 and the arrete of 12 July 2024, on an experimental basis until 31 December 2034, for laundry, indoor floor washing and vegetable-garden watering. Not permitted for drinking, cooking or bathing.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Direct greywater diversion to toilet flushing (This page) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: None · Upkeep: None · Change to daily life: Daily · Works without the grid: Yes Choose it if you want to flush the toilet with shower water, with nothing to install or treat.
Subsurface irrigation reuse Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you want your garden watered for free with your cleaned greywater.
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.