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?
Cistern-lid handwash basin (handwash water reused for flushing)
Passive
Note: Cost, carbon and footprint are broad judgements against comparable building approaches, not measured figures.
What your site needs
An existing cistern-type WC whose lid the unit can replace or sit on, and a pressurised cold supply already feeding that cistern
A small basin on the toilet cistern lid, fed by the cistern’s own fill pipe. You wash your hands in clean drinking water, and that water drains into the cistern for the next flush. One lot of water does two jobs, saving about 1.5 litres per handwash, with no new plumbing.
15-25 years for the basin and fittings, matching standard sanitaryware; the fill-valve diverter and the strainer are the earlier-wearing parts
Embodied carbon
Low
Space / material use
Low
Output timing
On-demand/controllable
Skill to repair
Basic
Regulation (FR example)
Sold in France as an off-the-shelf sanitary fitting. The reuse happens inside a single appliance rather than through a building-scale greywater network, which is the case French greywater-reuse rules are written around, but treat that as the practical position rather than a verified legal reading, and confirm locally before relying on it.
How does this solution compare to others for the same need?
The only option catalogued for this need so far, so there is nothing to compare it against.
Sources
Reutilisation Eau, lave-mains integre aux WC (independent explainer, gives the per-wash and annual savings figures)
WiCi Concept, kit lave-mains adaptable sur WC (French manufacturer of the adaptable kit; commercial source, product detail only)
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.