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In the pathway: Urban permaculture

Greywater

Wastewater from the shower, the sink or the laundry, usable in the garden.

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Explanation

With biodegradable soaps and suitable filtration (planted basins, gravel, sand), greywater can irrigate trees, hedges or planted strips. Beware of local regulations and avoid it on crops eaten raw. An approach systematised by Brad Lancaster (Rainwater Harvesting for Drylands, 2006-2008) and Art Ludwig (Create an Oasis with Greywater, 2007).

Refined definition

Greywater groups together all domestic wastewater that is NOT sanitary: shower, sinks, washing machine, light kitchen sink. To be distinguished from blackwater (toilets), which is heavily contaminated and requires full treatment. Greywater contains few pathogens, mainly residues of soap, skin, hair and light food, directly usable after simple filtration.

Key points

  • Three levels of complexity

    LEVEL 1: Direct bucket collection from the shower, occasional use on fruit trees. LEVEL 2: Gravity diversion to a tree mulch bed, Branched Drain (Art Ludwig), simple, no pump. LEVEL 3: A reed-bed filter (Phragmites australis) + a buffer basin + redistribution, a capacity of 5-200 L/day, for washing-machine or shower water. Sources: Brad Lancaster, Rainwater Harvesting for Drylands and Beyond, Vol. 1 and 2; Art Ludwig, Create an Oasis with Greywater.

  • Choosing the soaps

    For use in greywater destined for the garden: favour soaps without sodium, without boron, without EDTA. Prefer Marseille soap, Aleppo soap, homemade laundry (black soap + bicarbonate + washing soda). TO AVOID: fabric softeners, chlorine bleaches, synthetic fragrances, antibacterials (triclosan). Practical consequence: switch to a compatible eco-friendly laundry detergent before installing a greywater system.

  • French regulations

    In France, reusing your greywater at home is governed by decree no. 2024-796 and the order of 12 July 2024: the system must be declared to the prefect before it is first used. Permitted uses: toilet flushing, decorative fountains, cleaning outdoor surfaces and washing vehicles at home, watering green spaces at building scale. Washing laundry, cleaning indoor floors and watering vegetable gardens are only possible on an experimental basis, until 31 December 2034 and with the prefect's authorisation, under the conditions set by an order of 29 July 2026. This framework is evolving: check the text in force on Légifrance before any installation.

Watch out for

  • • NEVER spread greywater directly on crops eaten raw (salad, strawberry, leafy vegetables).
  • • Distribution pipes: prefer them underground at 10-15 cm depth, under mulch, free-standing water attracts mosquitoes and presents a health risk.
  • • NEVER store greywater for more than 24 h: it ferments quickly and becomes foul-smelling and dangerous.

Examples

  • • Reed-bed filter
  • • Branched Drain (Art Ludwig), gravity distribution
  • • Underground irrigation of fruit trees
  • • Phytopurification basin
  • • Ecological soaps only (Marseille, Aleppo)

Sources

  • Lancaster, B. (2019). Rainwater Harvesting for Drylands and Beyond, vol. 1 (3e éd.) et vol. 2 (2e éd.). Tucson : Rainsource Press.
  • Ludwig, A. (2006). The New Create an Oasis with Greywater (5e éd.). Santa Barbara : Oasis Design.