Passive
A shallow black basin of water under a sloping sheet of glass. The sun evaporates the water, it condenses on the underside of the glass and runs down into a channel. This is distillation rather than filtration: what comes out is very nearly pure water, because salts, minerals, heavy metals, sediment and pathogens cannot become vapour and simply stay in the basin. The catch is the other half of the same principle. Anything that IS volatile at these temperatures travels with the steam, so light solvents and some organic compounds pass straight through, and a still is the wrong answer to those. It is the right answer to salt, which nothing else here removes. Slow and area-hungry: output follows the sun and the surface, not demand. The product is also mineral-free and flat to drink, which matters if it is the only supply rather than a backup.
One of 5 ways to meet Treatment / purification. Build 1/5, Upkeep 1/5, Efficiency not rated. Cost, carbon and footprint below are rated against those 5, not in absolute terms.
Unshaded south-facing ground or roof area, sized to the water wanted
Every option in this sub-function, with the value on each axis and a note on what drives it (this solution highlighted):
| Solution | Build skill | Upkeep burden | Efficiency |
|---|---|---|---|
| Multi-stage filtration + UV disinfection | Intermediate | 7 | #2 |
| Bio-sand filter | Basic | 4 | #3 |
| Ceramic candle filter (silver-impregnated) | Basic | 4 | #3 |
| Reverse osmosis (RO) filtration | Specialist | 8 | #1 |
| Solar still (solar distillation) | Basic | 2 | N/A |
Build skill and upkeep burden are proxies (lower burden = simpler to maintain); the efficiency column is this sub-function’s ranking, 1 = best. “N/A” where an axis isn’t rated here.
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.