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💧♻️ Greywater reuse
Naturally treating and reusing a household's greywater (shower, sink, washing machine — never toilet waste) on site, through a simple gravity-fed filter system (settling tank, aerator, planted filter trench, polishing pond) instead of letting it run needlessly into the sewer or a soakaway.
When should you do this?
Spring or early summer, so the trench and pond plants establish before the next winter frost
What will you need?
- Two-chamber greywater digester tank (sized roughly 500-1500 liters per person)
- An inverted-elbow overflow filter to hold back floating debris
- An aerator (bubbler) tank, 30-50 liters per person
- Washed river gravel for the planted filter trench
- Waterproof plastic liner for the trench and pond
- Aquatic/marsh plants (reeds, sedges, sweet flag)
- Spade, wheelbarrow
How to get started?
- Map out which household drains actually produce greywater (shower, sink, washing machine) — never route toilet waste (blackwater) into this system.
- Install a two-chamber settling/digester tank for the incoming greywater, sized at roughly 500-1500 liters per person.
- Fit the tank's overflow with an inverted-elbow pipe, so only the clearer, lower layer of water passes on while floating grease and debris stay behind.
- Build an aerator tank to add oxygen to the water, sized at roughly 30-50 liters per person.
- Dig a planted filter trench about 80 cm wide and 40 cm deep, line it with waterproof liner, and fill it with washed river gravel.
- Plant aquatic/marsh plants (reeds, sedges) in the trench — their roots and the microorganisms around them further purify the water.
- Route the trench's overflow into a polishing pond (at least 3 m³, roughly 1.5-2 m² of surface per person), also lined with liner and geotextile.
- Plant aquatic plants in the pond too, giving a clean, attractive final stage — the water soaks into the ground or evaporates from there.
- Check and clean the filter trench yearly, and prune/maintain the plants.
Useful tips
- The system is fully gravity-fed, no pump needed — pay close attention to slope when planning it.
- Don't let strong chemicals, bleach, or large amounts of grease into the greywater — they can harm the filter's microbial life.
- The method comes from the EAUTARCIE ecological wastewater treatment system — worth reading up on before scaling it up.
Ready? Start a greywater reuse project, or join one already running near you.