What is blackwater?
Blackwater is wastewater from the toilet: flushing water containing urine, faeces and toilet paper. It is the opposite of greywater, the less polluted wastewater from showers, baths, washbasins and washing machines.
Difference from greywater
| Blackwater | Greywater | |
|---|---|---|
| Source | Toilet | Shower, bath, washbasin, washing machine |
| Pollution | Heavy, with pathogens | Lighter, but with soap and grease |
| Reuse | Only after intensive treatment | After treatment, for example for toilet flushing |
Drainage in an ordinary home
In most homes black and grey water come together in the internal drainage and flow through the public sewer to a wastewater treatment plant. Where there is no sewer connection, the wastewater goes to a septic tank or an individual treatment plant.
Separate collection
In some sustainable neighbourhoods blackwater is collected separately:
- Vacuum toilets use very little flushing water, so the blackwater stays concentrated.
- The concentrated blackwater is digested, producing biogas.
- Nutrients such as phosphate can be recovered from the residue.
Such a system needs a separate blackwater pipe and a central plant in the neighbourhood.
Practical points
- Never reuse without treatment: blackwater contains pathogens and must not go on the garden or into a rainwater system.
- Separation in the home: if you want to reuse greywater, keep the black and grey water pipes separate up to the point of treatment.
- Traps: every outlet needs a trap to keep sewer gases out.
- No fat or wet wipes: they cause blockages, including in vacuum systems.
Related terms
- Greywater
- Waste water
- Sewer
- Septic tank
- Drain trap
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