untreated waste water (as from sinks. baths. or washing machines) that does not contain human wastes (as from toilets) that can be used for landscape irrigation.

graywater (Wikipedia)
Left: Greywater sample from an office building. Right: Same greywater after treatment in membrane bioreactor

Greywater (also spelled graywater, grey water and gray water) or sullage is all wastewater generated in households or office buildings from streams without fecal contamination, i.e. all streams except for the wastewater from toilets. Sources of greywater include, sinks, showers, baths, clothes washing machines or dish washers. As greywater contains fewer pathogens than domestic wastewater, it is generally safer to handle and easier to treat and reuse onsite for toilet flushing, landscape or crop irrigation, and other non-potable uses.

The application of greywater reuse in urban water systems provides substantial benefits for both the water supply subsystem by reducing the demand for fresh clean water as well as the wastewater subsystems by reducing the amount of wastewater required to be conveyed and treated. Treated greywater has many uses, for example toilet flushing or irrigation.

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