Grey water is waste water generated in households or office buildings from streams without Sewage contamination. As grey water 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 grey water 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.
Grey water, by definition, does not include the discharge of toilets or highly contaminated waste water, which is designated as sewage or black water to indicate it contains human waste.