What it is
Greywater is gently used water. Showers, baths, bathroom sinks, washing machines.
It excludes toilet water (blackwater) and kitchen water (grease, food). In most homes it accounts for 50 to 80 percent of indoor use, and almost all of it flows straight to the sewer.
A family of four produces 300 to 400 litres of greywater a day. That is enough to carry a small food forest through a dry summer without touching the mains.
Why it works
Soil eats greywater. Soap residue, skin cells, and organic matter feed the microbes already there. Within hours the water is clean.
The trick is delivery. Subsurface, slow, and mulched. Above ground it pools, smells, and breeds problems.
Check local codes before you cut a pipe. Simple laundry systems are unpermitted in many places. Shower reroutes usually are not.
Laundry to landscape
The simplest build. No permit in most jurisdictions, no extra pump, one afternoon.
The washing machine's internal pump pushes water through a three-way diverter valve and out to the garden through 1 inch polyethylene tubing. Switch the valve to sewer when you wash nappies, paint clothes, or anything ugly.
The basins. Shallow depressions 30 to 50 cm wide around each fruit tree. Fill with coarse wood chip. The chip filters the water and keeps it off the surface. Split the line with tee fittings so one cycle waters three or four trees.
The soap. Plant-based, biodegradable, no sodium, no boron, no chlorine bleach. Skip anything labelled antibacterial. Oasis and Ecover work. Most supermarket detergents will salt your soil in a year.
Shower and bath
Shower water is the cleanest greywater stream. Mostly warm rinse with a little soap and hair.
Reroute the drain through a surge tank. A 60 litre drum, inlet near the top with a mesh screen, outlet near the bottom. Showers dump water in short bursts; the tank buffers them into a slow release the soil can absorb.
The tank empties inside 24 hours. Longer than that and it turns anaerobic and stinks.
Send output to subsurface lines or mulch basins. Never to sprinklers. Never to drip emitters that sit on the surface. Greywater does not touch leaves, fruit, or skin.
Where it goes
Good recipients: fruit trees, berry bushes, nut trees, ornamental shrubs, banana circles. Their fruit hangs above the soil and their roots run deep.
Bad recipients: lettuce, carrots, strawberries, herbs, anything you eat raw at ground level.
Rotate zones. Watering the same three trees every wash builds salt over years. Move the basins or split the manifold.
When it goes wrong
Soil pH creeps up. Most soaps are alkaline. Test annually. If pH passes 7.5, mulch with pine needles or work in elemental sulphur.
Sodium damages clay. Detergent salt collapses soil structure. Switch to sodium-free brands and dust gypsum into the basins once a year.
The basin pools. Chip is too fine or the line is overloaded. Dig deeper, add coarser mulch, or add another basin downstream.
Someone gets sick. Flip the valve to sewer until the household is clear. Gastrointestinal bugs travel in greywater.
See also
- Rainwater harvesting basics for the clean-water half of the household supply
- Food forest design for the landscape that drinks greywater best
- Swales on contour for moving the overflow across slope
- Mulch for moisture for the chip layer that makes basins work
- Drip irrigation for clean-water lines that share the same trees