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Theodore Ray
Planning and development surveyor
Asked a question 2 years ago

What is the difference between Gray Water and Black Water in Sewers?

What is the difference between gray water and black water in sewage? How can we differentiate between them in a sewer?

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Terry Collins
Sustainability consultant

Very precise answer. Lot of information specially the treatment of the grey and black water is very much informative.

Difference between Black Water and greywater:

Black Water:

Blackwater is the best water from bathrooms and toilets that contains faecal matter and urine. Waterproof kitchens and dishwashers are also considered Black Water due to the contamination of pathogens. It is also referred to as she waits for groundwater and can carry diseases and bacteria both of which could be harmful.

Treatment of blackwater:

The biological or chemical treatment and infection are required for treating Black Water.


Greywater is the best water that comes from sinks, washing machines, bathtubs and showers. Greywater contains a very low level of contamination and making it easier to treat and process. Recycled greywater is commonly used in irrigation and constructed wetlands as long as no harmful chemicals are present.

Treatment of Greywater

Greywater can be reused in cartoons with little or no treatment subsurface irrigation system to evenly spread water around in the garden. This method is very safe for treated greywater.

Thank you.

Seth Morgan
Construction Superintendent

The difference between gray water and black water in sewers are as follows:

Gray water :- Gray water is all of the waste water that drains from your shower and kitchen and bathroom sinks. Gray water has some bacteria but it can be filtered and reused in gardens or lawns, if done properly.

Black water :- Black water contains human waste and is unsafe. It must be stored in its own tank and disposed of very carefully.

Henry Newman
Water resource engineer

You explain it very well.I liked it very much Thank you.


Please find the difference between grey and black water in sewage systems.

TypeContaminated or Used Water have chemicals and no sewageUsed water with sewage content.
CompositionChemicals – [No fecal contamination]

Sewage rich in organic materials, micro-nutrients, and nitrogen



SourceBath, shower, sinks or washing machinesKitchen sinks or toilets 

Sand filtration, lava filter systems, controlled wetlands and living walls.





Biogas Settler, Imhoff Tank, Anaerobic Baffled Reactor (ABR), Anaerobic Filter, Waste Stabilisation Ponds, Aerated Pond, Free-Water Surface CW, Horizontal Subsurface Flow CW, Vertical Flow CW, Trickling Filter, UASB Reactor, Activated Sludge.




Thank You and Regards

Definitely, it helps me in understanding the difference.Thanks.

Gray water: It is water that comes from the kitchen sinks, bathrooms, bathing water, water from washing clothes, utensils, or any other wastewater which does not contain feces of humans or other animals.

Blackwater: It is now apparent that it is water which contains feces of animals and humans, it is water from urinals, toilet seats, commodes, etc. is called black water

And to tell the difference in the sewer is hard because it generally mixes in the sewer, if not provided with different outlets.

I hope this helps!