Greywater, is generally accepted as being wastewater generated from wash hand basins, showers and baths, which can be recycled on-site for uses such as WC flushing, landscape irrigation and constructed wetlands. Greywater often excludes discharge from laundry, dishwashers and kitchen sinks due to the high nutrient levels.

Most Greywater is easier to treat and recycle than black water, because of lower levels of contaminants. If collected using a separate plumbing system from black water, domestic Greywater can be recycled directly within the home, garden or company and used either immediately or processed and stored. If stored, it must be used within a very short time or it will begin to putrefy due to the organic solids in the water. Recycled Greywater of this kind is never safe to drink, but a number of stages of filtration and microbial digestion can be used to provide water for washing or flushing toilets. Some Greywater may be applied directly from the sink to the garden or container field, receiving further treatment from soil life and plant roots. Given that Greywater may contain nutrients, pathogens, and is often discharged warm, it is very important to store it before use for irrigation purposes, unless it is properly treated first.