I’ve spent the last couple of days trying to wrap my head around the implementation of a gray water recovery system for the earthship. The information provided in the Earthship volumes by Mike Reynolds is not detailed, and as gray water recovery is not a common building practice it is difficult to find information on this topic.

First a bit of background … Fresh water (from a well or rainwater cache) is degraded after it is used residentially; it becomes either black or gray water. Black water refers to the outflow from toilets, which contains fecal matter and is difficult to treat. Gray water is the outflow from the remaining plumbing fixtures in the house; sinks, showers, baths and laundry. This water is easier to treat and it is this water that we will be recovering in our gray water recovery system.

From my initial research the regulatory work done on gray water systems in Canada is only at beginning stages, and deals mostly with the recovery of gray water for later use in flushing toilets. This model of gray water recovery stresses the chlorination/treatment of the gray water so that it can be stored for later use. This is an expensive process requiring chemicals, storage and pumping that is not what we are interested in. Our intention is to contain, filter and then use the gray water in a constructed wetland environment located in our residence. The gray water will be purified in this environment and used to grow plants and fruit trees. This basic approach is described in Earthship Volume 3, but as I said earlier, the implementation details are vague.

In Canada the CHMC (Canadian Housing and Mortgage Corporation) is doing some research into gray water systems, and seems to be involved in defining standards. Cate Soroczan is listed as the Project Manager on much of this work and would seem to be a useful contact. I intend to start with the CHMC to determine what regulations govern the implementation of a gray water system in our jurisdiction and what standards exist.

My other approach to investigating gray water was to try and determine generally accepted construction methods and practices with regard to gray water recovery. As gray water recovery is not used in mainstream North American construction there seem to be a lot of conflicting opinions and practices in this field. The work of Art Ludwig is referenced often on the internet by various organizations (The Real Goods for one) and people, and as it turns out he has two books out on the subject; ‘Create an Oasis with Gray Water’ and the ‘Builder’s Gray water Guide’. I have decided to pin my hopes on Art Ludwig’s experience and have ordered these two books (www.oasisdesign.net). Hopefully, when these two books arrive I can start laying out a gray water recovery system in earnest.

In the meantime I think I have tracked down enough information to flesh out the square footage and basic layout required of a gray water system for my family of five. This should allow me to carry on with drawing my plans and ensuring that I have allocated enough space for gray water recovery and located the system logically in our home. The initial information on gray water that I will be using in my design is 35 gallons per day / per person of gray water generated residentially, and from .14 – 1.2 sqft of gray water ‘mulch field’ per gallon of gray water generated per day.

In other words, my family of five will generate 175 gallons of gray water per day, and the gray water field will need to be 24.5 sqft on the low side to 210 sqft on the high side. For the time being I am going to stick to the upper end of this estimate and design a gray water field of approximately 200 sqft. With this information in mind I have modified my plans as detailed in the attached drawing. I will modify them again as I learn more about gray water.

Most of the changes in this iteration of the plans are based on layout and our ultimate preferences. We re-arranged the kitchen and pantry for better work flow. Sandra wanted easy access to the outside from the kitchen so we added a vestibule and door in the middle. We have added a second toilet so that we are not all lined up to use the bathroom. I cannot easily figure out how to move the second bathroom closer to the master bedroom given the constraints imposed by the water system. Sandra and I have agreed we can live with this layout.