Rainwater harvesting and storage

Collects roof runoff; simple and low-tech, but supply varies with rainfall and needs treatment before drinking. Roof surface accumulates dust, pollen, and bird droppings between rain events, concentrated in the first flush of each storm; a first-flush diverter (discarding roughly the first 1-2mm of roof runoff) is the standard, low-tech mitigation and should be assumed as part of this solution, not a separate add-on.

Cost

Low

Upkeep

Seasonal

Skill to build

Basic

Lifespan

Roof/gutter collection surface: matches roofing material lifespan; the tank itself per the elevated cistern/tank storage figure

Embodied carbon

Low

Space / material use

High

Output timing

Continuous process

Skill to repair

Basic

Regulation (FR example)

Non-potable water indoors is governed by decret 2024-796 and the arrete of 12 July 2024 (in force 1 September 2024, replacing the arrete of 21 August 2008). Permitted uses include toilet flushing, indoor floor washing and garden watering at building scale. Drinking, cooking and bathing are not permitted. A declaration to the mairie is required where the building is also connected to the public network.

Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.

What your site needs

A roof area and material suitable for potable-adjacent collection (avoid lead flashing, treated shakes)

Inputs

• Rainwater

Outputs

• Unheated Water

Sources

• First-flush diverter mechanism source already cited (Sources-and-References #21)

Tutorials

• https://wiki.lowtechlab.org/wiki/Récupérateur_d'eau_de_pluie
• https://wiki.lowtechlab.org/wiki/Dimensionner_la_récupération_d'eau_de_pluie_pour_être_autonome

What this page does not tell you

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.