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Greywater Reuse

Wastewater from sinks, washing machines, and dishwashers can be treated and reused

Diagram of a greywater reuse system.

Greywater is wastewater from bathtub, shower drain, sinks, washing machines, and dishwashers. Greywater accounts for 60% of the outflow produced in homes. It contains little or no pathogens and 90% less nitrogen than black water (toilet water). Because of this, it does not require the same treatment process. By designing plumbing systems to separate it from blackwater, greywater can be recycled for irrigation, toilets, and exterior washing, resulting in water conservation. When planned into new residential construction, the home's wastewater treatment system can be significantly reduced, resulting in cost and space savings.

Systems generally consist of a three-way diverter valve, a treatment assembly such as a sand filter, a holding tank, a bilge pump, and an irrigation or leaching system. The holding tank cools the water and temporarily holds it back from the drain hose. Systems can either be custom designed and built, or purchased as a package. Techniques include recessed or raised planter soilboxes, water injection without erosion, gravity or pressure leach chamber, and irrigated greenhouses. Some system components can retrofit existing irrigation systems.

Environmental Performance

Greywater does not require the intensity of treatment that blackwater requires to neutralize it. Separating the two types of flows saves conveyance, infrastructure, and chemical expense where offsite sewer treatment is provided.


It is relatively simple to separate grey and blackwater drains in a new construction application. One-story homes on a crawlspace or basement foundation may present an opportunity for simple retrofit of greywater piping, but the feasibility of remodeling for greywater reuse should be examined on case by case basis.

Onsite systems that will utilize gravity for outfall flow require the same attention to detail required for septic system layout.

Costs for the house drain pipe of a greywater system are minimal if the greywater system is installed with the DWV rough-in while a home is under construction. A 2 ½ bath home would require less than one half day of a plumber’s time and some drain pipe material. Dependent upon location, this could be in the $325-495 range. Because municipal codes are still evolving on greywater reuse, it is possible that the greywater drain would initially be installed to outflow into the main plumbing stack for future retrofit to a separate outfall.

In jurisdictions that will allow an active onsite treatment system, infrastructure installation can cost from $1,500 to $2,500.

There are no additional costs anticipated from the drain pipe side of a greywater system.

It is likely that jurisdictions that will allow onsite greywater reuse will require a monthly maintenance contract on the system, which would include water sampling. Indications are that a monthly service contract would run between $35-60.

Local regulations, sanitary engineers, inspectors, and boards of health might not be familiar with or permit these methods. Greywater separation might also not be justification for downsizing the septic system.

Chapman Companies: Rancho San Marcos, Santa Fe, New Mexico

Because conventional wastewater plumbing lines combine black and greywater, separating the two generally involves a parallel wastewater system. Space must be available for larger components such as a holding tank or some filters, which can be located in a basement, shed, or possibly outside.

Varies with equipment used and maintenance provided.

Local regulations, sanitary engineers, inspectors, and boards of health might not be familiar with or permit these methods..

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.