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Indoor Gray Water Reuse, Cascading,
Gray Water Heat Recovery, and Rainwater Harvesting

Summary: Case studies, links, and references for indoor graywater reuse.

On this page:


Indoor gray water reuse

Canada Mortgage and Housing Corporation

The North American leader in pioneering indoor gray water reuse. Contact: Cate Soroczan.

Environmental Impact Assessment Tools for Multi-Unit Housing
Water Recycling Demonstration
Onsite Recycled Water Quality Monitoring
gray water Technology Software Development
Discussion Paper on Water Reuse - Needs, Trends, and Case Studies
Quayside Village gray water Demonstration Project Status
: Ongoing A gray water system similar to that of the Toronto Healthy House system is being implemented into a 19 unit cohousing project in North Vancouver, B.C. This system will be capable of treating gray water from sinks, laundry, and showers for reuse in showers, laundry, and toilets. Initial testing will be restricted to toilet reuse only. Double plumbing has already been installed and the gray water system is being installed following the signing of a contractual agreement between the city and development regarding ongoing monitoring and maintenance. Upon completion the system will be subject to continuous online water quality monitoring and laboratory analysis to ensure that the both the system and the online monitoring is working to satisfaction. Researcher: Cate Soroczan

Conservation Co-op Residential Water Reclamation

Treated shower and bath gray water reused for toilet flushing in a 4 story, 84 unit apartment building located in downtown Ottawa.

  1. Canada Mortgage and Housing Corporation, 1997, "Regulatory Barriers To On-Site Water Reuse, Canadian Water and Wastewater Association", Ottawa, Ontario.
  2. Totten Sims Hubicki Associates, 1998, "An Application Guide For Water Reuse Systems", Canada Mortgage and Housing Corporation, Ottawa, Ontario.
  3. Totten Sims Hubicki Associates, 1999, "On-Site Water Reuse In Canada - Ottawa 1999 Protocol", Canada Mortgage and Housing Corporation, Ottawa, Ontario.
  4. Totten Sims Hubicki Associates, 1999, "Water Quality Guideline And Water Monitoring Tools For Residential Water Reuse Systems", Canada Mortgage and Housing Corporation, Ottawa, Ontario.
  5. Townshend, A.R., 1993. " Advancing the Light Grey Option. Making Residential gray water Reuse Happen." Canada Mortgage and Housing Corporation. Ottawa, Ontario.
    For additional details on this and other water reuse treatment research reports please contact Canada Mortgage and Housing Corporation.


Toronto healthy house

A three bedroom house on a small lot with no sewer or water supply grid connection. Reuses treated combined wastewater for all-non potable uses.

Excellent description by Rolf Paloheimo, Creative Communities - Research Builders - Developers 26 Garnock Avenue, Toronto, Ontario M4K 1M2 and Bob LeCraw Presented at Disposal Trenches, Pretreatment, and Reuse of Wastewater Conference sponsored by the Waterloo Centre for Groundwater Research and the University of Waterloo May 13 1996

Regulatory barriers to on-site water reuse in Canada


Adam Joseph Lewis Center, Oberlin College Oberlin, Ohio

The Lewis Center's living Machine treats wastewater using a system of engineered ecologies that include microbes, plants, snails, and insects, and is designed to treat up to 2,000 gallons of the building's wastewater daily in a beautiful, garden-like atmosphere. Upon completion of a water pressurization system, the treated wastewater will be recycled back through the building for non-potable reuse.


Building 850 Naval Construction Battalion Center Port Hueneme, CA

Low-rise office and computer facility 1998, 45% energy & water savings compared to existing building, major renovation & addition to existing building, daylighting, shading, photovoltaics, solar space & domestic hot water heating, high efficiency lighting with dimming/ photo sensors/ occupancy sensors, natural ventilation, natural gas heat pump air conditioning, underfloor air distribution, heat recovery from air conditioning system, high efficiency pulse boilers, gray water reuse, rainwater harvesting, water conserving irrigation, IAQ monitoring, recycled & reused building materials, low toxic materials. Contact: Scott Ellinwood Associates (architect)

David L. Lawrence Convention Center expansion Pittsburgh, PA

Northeast Urban Low-rise convention center and offices Partially reuse existing structure, urban infill, natural ventilation, low temperature air delivery, displacement ventilation, raised floor air supply plenum in meeting rooms, daylighting, spraying water evaporative cooling of roof, environmentally preferred materials, ice storage, geothermal cooling, gray water recycling. Contact: Rebecca Flora of Green Building Alliance 412-431-0709 Dori Landry, Burt Hill Kosar Rittelmann Associates, 202-333-2711

EPICenter Montana State University Bozeman, MT

North Semi-rural Low-rise education, research & office building 2000, still in design, Passive ventilation, passive heating and cooling, daylighting, fuel cells, photovoltaic panels, rainwater harvesting, solar aquatic wastewater treatment, sustainable materials, advanced glazing, intelligent building system controls, going for platinum LEED. Contact: Kath Williams of MSU, 406-994-7713

Gray Water/ Wasser Recycling (Germany)


Pilot plant in Berlin We developed several gray water plants in Block 103, Berlin-Kreuzberg, in cooperation with STATTBAU, an ecological program financed by the state of Berlin and the Federal Ministry of Building. These plants have been in operation since 1989 and have been investigated and optimized extensively by the Department of Hygiene of the Technical University of Berlin. The results of many years of research have been invested in the development of these graywater plants. EXPO 2000, Hannover The German construction company BauBeCon and the local public utilities erected a gray water experimental park in Hannover, HÕgewiesen. A gray water plant with a two-stage RBC (rotating biological contactor) was erected to provide for 6 housing units, and its successful operation has been documented by the municipal wastewater / drainage works since November, 1994. 4-star hotel 'Arabella' Commissioned by the Bavarian Industrie und Gewerbe Bau GmbH & CO, Munich, a six-stage gray water plant, one of the first of its kind worldwide, was installed in the 4-star hotel 'Arabella' for 400 beds. With a cleaning capacity of 20,000 liters a day, this plant has been in operation since January, 1996. Demonstration plant in Kassel A two-stage RBC, sized for 60 individuals, was erected in Kassel-Hasenhecke for 'Wohnstadt', the largest housing construction company in North Hessen. This plant has been in operation since the spring of 1996, and is being compared with rainwater reuse plants in a program initiated by the state of Hessen to compare water-saving technologies.


The path of water in an Earthship:

  1. Water is caught from roof catchment systems and channeled via silt catches into cisterns.
  2. Cisterns gravity feed a DC pump and filter panels (see WOM).
  3. Pump and filter panel (WOM) pushes water into a pressure tank and conventional household water pressure is the result.
  4. The Toilet is separated from drainage system of all other household plumbing fixtures.
  5. Water is used in a conventional way such as bathing or washing dishes.
  6. This water is then drained through a grease and particle filter into linear biologically developed interior gray water treatment and containment systems. This produces an interior tropical plant jungle that facilitates filtering, oxygenation, evaporation, and transpiration of the water. Due to varying severe winter conditions, we have opted to treat the bulk of the water inside the passive solar heated building which provides tropical temperatures for year round treatment of the water. The net result here is that the water is cleaned up while breathable oxygen producing food and flora plants are supported inside the dwelling. At the end of this treatment system, the gray water is recollected in a well where it tests below measurable nitrate levels.
  7. This clean looking (but not drinkable) water is now piped back to flush the toilet (toilets) with.
  8. Next the water goes outside to a conventional septic tank that is solar heated with a glazed south side to enhance the anaerobic process. This unit functions like a regular septic tank (only better) with a line out to a conventional leach-field. We add a preferred but optional line out that goes in to rubber lined exterior plant cells (size and quantity varies) that are constructed very similar to the interior gray water treatment and containment planter. This facilitates total containment of remaining effluent and directs its use toward exterior landscaping. After this use the water again tests below measurable nitrate levels

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Water cascading

Toto handwash cascade toilet

Toto handwash cascade toilet Traditional Japaneese toilet with reuse of handwash water for flushing.

If you can read Japanese maybe you can find the toilet above on this site somewhere. The other image is from an older model Japanese handwash toilet.

In this hygienic, water saving design a portion of the flush water passes automatically through the handwash basin on its way to the toilet bowl.

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General gray water information

Very extensive, focused on outdoor reuse.

Includes water quality information.

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Gray water heat recovery

Gray water heat exchanger

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Rainwater harvesting

General information

Disney Conservation Learning Center, Disney Wilderness Preserve Kissimmee, FL

Southeast Rural Low-rise learning, administrative & laboratory facility Natural ventilation, operable windows, east/west long axis, oak tree shading, 5' overhangs, low-e/double glazed windows, integrated photovoltaics, geothermal heat pump, zoned HVAC, high efficiency lights, daylighting, environmentally preferred materials, low-VOC paints & stains, wood from sustainably managed forest, rainwater harvesting, construction waste recycling. Contact: Geoff Meyer Cooper Johnson Smith Architects, Inc. 813-273-0034

King Street Center Seattle, WA

Northwest Office, retail, parking facility 2000, sensor controlled lighting is one of most energy efficient in Seattle, high efficiency air filtration, C02 sensors, exhaust for copy rooms, largest installation of renewable carpet in North America, low-VOC paints/ carpet/ system furnishings/ adhesives/ cleaning supplies, panels, recycled content paints & tiles, rainwater harvesting supplies 60% to 80% of water for flushing toilets. Contact: Carolyn Duncan King County DNR 206-296-8304

Lady Bird Johnson Wildflower Center Austin, TX

Southwest Rural Low-rise galleries, auditorium, classrooms, gift shop, library, & research labs building Passive solar heating/cooling, pragmatic building orientation, recycled / reclaimed / excavated materials, rain-water harvesting. Contact: Laurie Zapalac of Overland Partners, Inc., 210-829-7003, laz©

McKinney Sustainable Elementary School project (Roy Walker Elementary School) McKinney, TX

Southwest Low-rise school In construction phase, rainwater collection, daylighting, wind energy, solar energy, geothermal heating & cooling, recycled materials, water habitat, reduced reliance on motorized vehicles, recycling systems, landscaping sensitivity, indoor air quality. Contact: SHW Group, Inc., Mike Elmore, 972-701-0700

Nidus Center for Scientific Enterprise (by Monsanto)

Creve Couer, MO Midwest Suburban Low-rise office & lab building Fall 1999, LEEDTM certified, 30% better than ASHRAE 90.1-1989, energy efficient envelope and HVAC, waste heat recovery, daylighting, local/low-VOC/recycled materials, "living" air filtering wall, rainwater harvesting, efficient plumbing fixtures, low water use landscaping, bicycle facilities. Contact: HOK, 800-788-5518, ext 2610

Sustainable Technology Center Friday Harbor, WA

Northwest Rural Low-rise office complex Completed 1995, photovoltaic array, solar hot water, radiant heat, highly insulated envelope, Hydroxyl waste water treatment, drip irrigation, recycled-content materials, rain water collection, bicycle parking & showers, electric vehicle charging station. Contact: Jim Sackett Seventh Generation Strategies, Inc. 360-378-8588

CCI Center Pittsburgh, PA

Low-rise office building Adaptive reuse of existing building; salvaged kitchen, wood, and brick; carpet from job overrun; retrofit cellulose; new R24 walls; R6 windows; AirKrete; air sealing; organic roof garden; heat recovery ventilation; gas powered a/c; cabling in accessible channels; BIPV saves $12K/yr; nontoxic finishes; Agriboard; rainwater harvesting; expect 4yr payback; construction waste management. Contact: Robert J. Kobet Green Building Services Consultants Inc. 412-431-4449 ext 225

Chesapeake Bay Foundation Headquarters

Phillip Merrill Environmental Center Annapolis, Maryland Northeast Rural Low-rise office building and conference facility Fall 2000, LEEDTM Certified, energy use is 50% less than ASHRAE 90.1-1989, existing footprint, geothermal, photovoltaics, natural ventilation, daylighting, solar hot water, passive solar, dessicant dehumidification, composting toilets, non-CFC/HCFC SIPs, recycled content /recyclable/local/low-VOC/low embodied energy materials, rainwater catchment, native plantings, porous paving, bicycle storage. Contact: Will Zachmann of Steven Winter Associates, 202- 628-6100


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