Reuse greywater, the wash water from sinks, baths and laundry but not toilets, by sending it fresh to the soil under mulch or through a buried pipe, never storing it, and never putting it on leaves or on any crop whose edible part touches it. Use plant-friendly soap, rotate the application area so salts do not build up, and match the flow to the area: one litre over one square metre is one millimetre of water. Treat it as a steady drought supply, not a clean one.
Greywater reuse is the use of lightly used wash water from sinks, baths and laundry, but not toilets, to irrigate garden plants through mulch basins or subsurface lines.
A Steady Supply, With Dirt And Salt In It
Greywater is available in dry years as well as wet ones, which is its value in a drought plan. It contains soap, food scraps, grease, hair and bacteria, and the soap and salts accumulate in soil. The carrier guide (Drought Resilience & Water-Efficient Agriculture) advises routing sink and laundry water through a mulch basin, using plant-based biodegradable soap, rotating application areas to prevent salt buildup, and never applying greywater to leaf crops eaten raw; it limits use to root crops and fruit trees. It also says greywater reuse can save 30-50% of household water use; that figure has no source and depends on what the household counts.
One of the carrier’s rules needs correcting. Root crops are in direct contact with the soil that greywater wets, and many are eaten raw or only lightly cooked, so they carry the same contamination risk as leaves. Put greywater on fruit trees and ornamentals, where the edible part hangs clear of the soil and the water, and keep it off anything eaten raw that touches the ground. Related guides: Garden Irrigation from Greywater, Mulch Basin Distribution and Greywater vs. Blackwater.
Worked Example: How Large An Area Can It Serve?
Illustrative inputs: 100 L/day of greywater; a fruit-tree area using 4 mm/day in the dry season.
- One litre over one square metre is one millimetre, so 4 mm/day is 4 L/m² per day. Area served: 100 L ÷ 4 L/m² per day = 25 m².
- Over a 90-day dry season: 100 × 90 = 9,000 L.
The inputs are placeholders. A mulch basin holds the day’s flow so it soaks in; if it does not drain within hours, the area is too small or the soil too tight.
What You Need
- A grease trap or screen at the source (Greywater Management).
- Piping to mulch basins or a buried distribution line.
- Plant-based soap, with no bleach, borax, or sodium-heavy detergent.
- Fruit trees or ornamentals as the receivers.
Method
Step 1: Separate the sources. Use sink, bath and laundry water, not toilet or diaper water, and not water from washing raw meat or sick people.
Step 2: Screen and trap solids and grease.
Step 3: Deliver by gravity to the mulch basin or buried line (Mulch Basin Distribution), under a thick layer of mulch, not by spray.
Step 4: Rotate basins so no spot gets all the flow.
Step 5: Flush with clean water or rain now and then so salts leave the root zone. In a dry climate there is no rain to do it.
Step 6: Watch the plants and soil. Yellowing, crusting, a slimy surface or a smell mean overloading; rest that basin.
Common Mistakes
- Storing it — it can turn foul and breed bacteria within a day or so.
- Spraying it — aerosols and leaf contact spread germs.
- Using it on edible leaves or roots eaten raw.
- Discharging it where it can run to a well or stream.
Safety
Greywater carries germs and chemicals
Greywater is not drinking water and can carry disease organisms and cleaning chemicals. Do not drink, store or spray it. Keep it away from wells, streams and children’s play areas, and wash hands after handling pipes and basins. Do not use it on crops whose edible part touches it.
What’s Next
- Learn next: Water-Efficient Irrigation — fitting it into the plan
- Combine with: Rainwater Collection and Storage — the cleaner supply