Greywater Bed

Greywater is water a household has already used for washing - baths, showers, bathroom sinks and the washing machine. It is roughly a third to a half of everything a house draws, around 340 litres (90 gallons) a day for a small family. A greywater bed sits at the far end of that plumbing, catching the flow before it reaches a septic tank or sewer and letting it soak into planted ground beside the house. Kitchen and dishwasher water stays out, since food waste makes it dirtier, and toilet water is sewage and goes elsewhere.

The bed is sized by the soil rather than by the volume of water, and the rule behind that is simple: water must never stand at the surface. Sandy ground takes it in quickly; heavy clay takes it slowly and needs a wider basin. The outlet is buried under at least 5 cm (2 in) of mulch, rock or soil so nobody touches the water, which is never sprayed and never stored - bacteria multiply in it within about a day. The bed does not so much clean the water as hand it to the soil and its living things. Plants differ in what they take: rosemary, roses, oaks and junipers cope well, azaleas and ferns do not, and vegetable beds carry a contamination risk that makes them unsuitable, root crops especially since the edible part sits in the wetted soil.

The slow failure is chemical, and it happens in the soil rather than the pipework. Wash water carries sodium, chlorine and boron, and sodium pushes calcium off the soil particles until the ground compacts and roots stop getting air. A bed run for years on the wrong soap ends as a bare hard patch, so detergent choice is part of the system: sodium-free, boron-free, chlorine-free, and liquid rather than powder. Upkeep is light: alternate greywater with fresh water so salts keep washing downward, and top up the mulch as it settles. Kept that way a bed lasts on the order of 25 years. Household reuse is widely regulated by a daily volume above which a permit is needed, worth checking first.