Greywater is wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater from toilets. Greywater is defined by its organic load, which is typically a combination of soap and waste. Greywater comes from sources such as sinks, showers, baths, and washing machines. It is different from blackwater, which is water that has come in contact with toilet wastes.
Greywater can be used for subsurface irrigation, toilet flushing, and underground disposal fields in some U.S. states that adopt the International Plumbing Code or the Uniform Plumbing Code. Greywater is fine for irrigating fruit trees or landscaping plants but should not be used on edible crops that touch the soil because it can contain harmful bacterial contaminants, grease, or residues of detergents. Greywater should be used within 24 hours of being collected because as the residues and contaminants break down, the water can start to pose health risks.
Greywater systems can be simple and use gravity to divert used water, or more advanced systems can pipe greywater over an extended area like a lawn or flower bed. Greywater systems leave some soap in the filtered water because it encourages growth and adds nutrients to the gardens soil.
