Water qualifies as greywater when it comes from a basin, shower, bath, laundry or kitchen sink and has not touched toilet waste, raw meat or blood, chemical cleaners or bleach, or diaper rinsing. Kitchen-sink water qualifies only after a grease trap, and laundry water only when soiled items and harsh detergents are left out.
Part of Greywater Recycling Systems
Qualifying as greywater means a drain’s water is allowed into the reuse system. The test is what the water has touched and what has been dissolved in it, not how it looks.
Sort At The Fixture, Not At The Garden
Once mixed in a pipe, water cannot be separated. The sorting happens where the water is made: separate drains for fixtures that qualify, and a separate way to deal with those that do not (Plumbing Separation).
Fixture By Fixture
| Source | Qualifies? | Condition |
|---|---|---|
| Hand basin | Yes | Plant-based or mild soap |
| Shower or bath | Yes | Hair and skin included; send to a filter first |
| Laundry | Yes, conditionally | Plant-based or mild soap; no diapers, no soiled or bloody items, no bleach |
| Kitchen sink | Yes, with precautions | Grease trap first; no raw meat or blood water |
| Toilet | No | Blackwater; composting system only |
| Diaper rinse | No | Blackwater |
| Water that touched raw meat or blood | No | Blackwater |
| Water with bleach, solvents or chemical cleaners | No | Harms plants and microbes in the treatment stages |
Those rows follow the parent page. The kitchen is “the most problematic greywater source”, as the parent page says, because of food particles, grease and food-borne organisms; some households route kitchen water to a separate system, which is a good choice if grease or meat handling is heavy.
Precautions The Parent Page Does Not State
- Illness. If anyone in the household has a diarrhoeal illness, send greywater to the dry well or soak pit, not the garden, until they recover. The wash water then carries the illness’s organisms. This is a precaution I add; the parent page does not set an illness rule.
- Wounds and sick-bed linen. Treat water from washing wounds or soiled linen as blackwater.
- The first rinse of a soiled garment. Take it to the blackwater route; rinse the rest as greywater.
Soap Decides Whether The Water Is Garden-Safe
The parent page lists plant-based soap (animal fat or vegetable oil with wood-ash lye) and castile soap as generally safe, salvaged commercial soap as usually fine in moderate amounts, and says to avoid boron-containing detergents (toxic to plants), bleach, antibacterial chemicals and sodium-heavy detergents (sodium damages soil structure). Check salvaged detergent labels for borax or boron and for high sodium. If you make your own soap (Soap Making), you can choose ingredients that are safe for greywater by design.
Cut The Load At The Source
- Scrape plates and pots dry before washing, and put scraps in the compost.
- Never pour fat or oil down any drain; wipe pans and keep the fat.
- Keep chemical cleaners out of the greywater drains; clean with soap and ash instead.
- Keep a hair catch in the shower and a strainer in the sink.
Common Mistakes
- Counting laundry as greywater regardless of what was in it. Diapers and bleach exclude it.
- Letting bleach down the sink “just once”. It kills the filter’s living layer and harms the garden.
- Thinking soapy water is clean. Soap hides, not removes, the dirt.
Safety
Chemical cleaners and blackwater in the stream poison plants, soil life and people
Bleach mixed with ammonia (urine, ammonia cleaners) releases toxic gas; never combine cleaners. Keep every blackwater source out of the greywater drains. Do not let anyone drink, cook with or wash food in greywater, however clear it looks.
What’s Next
- Learn next: Contamination Risks & Limits — what remains in qualified greywater
- Combine with: Grease Trap Design — the stage that makes kitchen water usable