Using Gray Water

Graham Bell has lived in Scotland since 1988, having previously spent ten years in London.  His work has taken him around Europe, Africa, the Middle East and the USA. He has a Master's Degree in Old English & Linguistics from Oxford University.  It took him many years to actually make the connection that most of what he does is dependant on the use of language, and to revalue that educational start point. Graham teaches sustainable design, and has written two books on the subject The Permaculture Way and The Permaculture Garden.  He frequently contributes articles to local, national and international media. He is actively involved in the cultural scene of Scotland, including Scottish Traditional music, song, art and woodwork.  He enjoys his garden, which supports a historic collection of Scottish apple cultivars and a wonderful range of bird life.   "Family is the most sustaining thing in my life.  After that comes the valuable network of people that I draw on for creative progress, both for myself and the people I work with.  Home is where the heart is." For more about Graham and his work visit www.grahambell.org.

Questions and Answers

Q: I have been reading up on gray water reuse as heat and as water for plants and gardens. I've been curious. Would the soaps used from the dishes, hand washing and showers/baths hurt the plants? I know that our soaps are non-toxic, but wouldn't they still harm plants? What about things that people wash down the drain like bleach or strong solvents?

A: (Penny Livingston-Stark) Soaps from hand washing, shower and baths will not hurt your plants if you run them through a simple filter of gravel. The main thing is the ph is too alkaline from the soaps. A gravel or wood chip filter will help that. Bleach and strong solvents are not ok for plants as they kill the bacteria in your filter. Gravel and wood chips are a medium for bacteria to live on. It’s the bacteria that is the filter. You do need to be mindful of what you put down your drain even if you don’t have a gray water system, as it STILL goes into the earth and groundwater somewhere if not in your garden.

Q: I am in the planning stage of building a cordwood house in Virginia. My design is decided on. I have plenty of wood, from clearing dead or dying trees on my land, and working for a realtor clearing plots and keeping the lumber. I am designing passive-solar for heating and cooling, and I plan to eventually have PVs for electricity. What I am not sure about is what to do about water. What are the best ways that you know of to consider as far as using:gray water/black water systemsStoragefiltrationpurificationcollection,etc.?

A:Penny Livingston-Stark) There are many ways to deal with gray water. The most common part of an answer to this question is “It depends”. Not knowing your full situation it’s a bit hard to answer but here goes….First it’s not a good idea to store gray water. If you do it will turn into black water. It’s important to use gray water as it’s available. For the least amount of maintenance I usually run it through a gravel filter in a lined trench to keep it isolated from any ground water and to be able to transport it to where you can use it. The size and shape of the trench depends on the volume of water you use. After it goes through the trench if it’s allowed to stay in the trench for about a week it should be treated enough go to your plants. You’l have to figure out how to get it to your plants as I have no idea about your site, slope etc. Gravity fed is best, you can use pipes from the gravel filter trench or just plant around the trench itself. If you use pipes, design it in a way that water loving roots can’t get in and invade. A valve box or an upside down five gallon bucket sunk with a hole for the pipe works. Valve box is best because you can check the pipe (it has a lid on it). Also most roots don’t like air and won't surface to go into the pipe. So the box keeps the gravel away from the pipe.

It’s best to use on perennial plants like fruit or nut trees, timber bamboo (if you can grow it there), berries, etc., as opposed to lettuce or leafy greens. You don’t want your food coming in direct contact with the gray water just in case Hepatitis C is around. (It can be a bugger to break down where other diseases don’t live long outside of the body.) For the least amount of maintenance I only use laundry and bath water. If you want to use kitchen sink you need to design a grease trap and a screen that you need to empty food chunks out of periodically.

Also you can catch water off of your roof. Just make sure you use an opaque tank and screens so critters can’t get in there an die. You can store roof water indefinitely if light can’t get to it.

Q: My son is trying to pick a good research question for his high school science fair project, a question that relates to using gray water for edible plants. Is there any smallish question that the Permaculture Institute would like him to research so that he is not reinventing the wheel and can contribute to the current knowledge on the subject? E.g.. Is there a kind of filter which would allow us to use gray water on directly on plants? Is there a way to change the ph of gray water? Are there dish and laundry soaps that are safe to use?

A: (Penny Livingston-Stark) I suggest he test the water before and after various treatments. He could run it through different mediums like gravel, pumice (if you can get it), wood chips, chopped bamboo, inoculated with marsh mud for the bacteria etc. Test it after 1 day, 2 days, 3 days. Etc. Then run it through a marsh plant system with rushes and cattails. He could also put it in a small “pond” at that point with duck weed and azola. You can test for a lot of things with a good koi pond tester. It won’t check for fecal coliform or surfactants; you need a lab for that.

Q: I am representing my my class from Mount Gambier North Primary School. We are a grade six class and we are wondering if you could give us some information on turning gray water into drinking water?

A: (Maya Madrigal) I am happy for your interest in gray water systems, and hope for your success in experimenting with the various techniques available. Gray water purification is an area with much experimentation, with some techniques being proven for several decades, while many remain unproven. First, I will clarify the term "gray water", which refers to water that has been used for showers, baths, sinks, and laundry. The term "black water" refers to water that has been used in water flush toilets. Do not confuse black water with gray water, it should not be used in any gray water system. The existence of the problem of black water is mediated by the use of composting toilet designs that allow for the use of harmless humanure in the landscape. Further, most gray water systems seek to purify water to a level adequate for landscape use, swimming pools, or for use in flush toilets, often the goal is not to use gray water to drink. The same reason for why we don't drink gray water is the same as for why we don't use black water. First, there are higher than normal levels of both nitrogen and various pathogens. The subjectivity of which pathogens will be present is variable or different depending on where you live, what levels and types of pollution and chemicals are present in your home or community.

For self-sufficient access to pure drinking water the most preferred method of collection would be from rain harvesting. What level of grease that is present also differentiates types of gray water, as if food particles from a kitchen sink, harsh chemicals or chlorine are present. I suggest that if you don't already, use biodegradable products for dishwashing, household cleaning, soaps and such, also use non-chlorine bleach. By using natural biodegradable cleansers we can protect the quality of our gray water, groundwater, and environment. I would suggest if you will be experimenting with gray water in a classroom or household setting, do not drink the water that has been purified.

You can compare different systems and water qualities through it's clarity, odor, and by using water testing tools available at pool or garden supplies to test pH, nitrogen, and other chemical and metal levels you find relevant (copper, chromium, cadmium, iron, lead, mercury, nickel, zinc). Basic gray water treatment relies on a combination of the following methods: AERATION using waterfalls, devices, wind, or gravity to make turbulence. SETTLING or allowing heavy particles to separate to the bottom of a tank. SKIMMING particles from the surface. FILTRATION. Biological uses of bacteria, phytoplankton and plants, adjusting the pH and using chemical ADDITIVES such as lime (calcium), salt, ferric sulfates (iron, sulfur).

A simple system would first trap sludge and grease using a septic type system which could use multiple stages. Next use a sand filter where the input is toward the bottom and the output is toward the top. Starting with the bottom layer pebbles, gravel, coarse sand, and fine sand. A soil bed planter box could next be used, very similar to the sand filter. First layer pea gravel for good drainage, put mosquito netting if you wish to keep separation from the sand, first coarse, next fine, then put a good two feet of humus rich top soil, into which you plant a garden. In cold climates green house beds could both filter and provide food. The output from this could even go into a pond system with turbulence, water plants, fish and of course beneficial microorganisms; this pond could also act as a natural swimming pool if designed properly.

A series of catch dams could store excess water above ground if necessary, while providing additional habitat. Or the water could be stored in sealed tanks, and/or connected to pumps and/or irrigation depending on the use and site specifications. I hope this brief description shows the infinite possibilities for gray water use, to not only recycle a precious resources but also we can gain from a diversity of benefits including crops, aqua culture, and recreation. I wish you a lot of fun experimenting with creating your own unique system for your classroom or home needs!

Q: My wife and I built a home in Northern Minnesota one year ago that utilizes a new and unique water system. We separate our gray and black water, compost the black water (toilets and garbage disposal sink) and treat our gray water to reuse it as potable water. We utilize rainwater for replacement/makeup water and have essentially eliminated any wastewater discharge from the building. We are reclaiming approximately 95% of the water and are operating the home on ~ 5 gallons of water (consumptive use) per day. Yes, it does use some energy, but our goal is to be net zero energy and wastewater discharge in the coming years. Are you aware of any other companies in the U.S. or abroad that are treating gray water to turn it into potable water on a household scale?

A: I have been in touch with a friend, Mark Moodie, who has many years experience with natural water treatment systems. He is well connected in the Steiner/Biodynamic movement (see the work of the Max Plank institute in Germany for example). I know a large number of other professional practitioners including several who have attended my own permaculture courses in the past. In the meantime here are some links to get you started in your investigation:

Well that'll keep y'all busy for a month or two...

Q: I live in Canada where we don't need any water for plants from Oct-April. Is it feasible to set up a graywater system that is used on plants during the summer but then goes into a regular septic bed over the winter? What else could we do with the graywater in the winter?

A: This is tricky to answer without a little more information. Key issues would be: Topography and land availability; Budget; How much do you care anyway?

So you can go from the simple cheap and cheerful to the exotic expensive and mindbogglingly clever with quite a few stops in between. But the simple answer is 'yes you can'.

You can fill barrels and keep it to the spring, but yucky and frozen water expands so the barrels may split.

When you mention septic tank I take it you have no mains drainage. You do not, however need to to put unwanted gray water into the septic tank. It could just go into a soak-away as there's nothing in waste food, detergent, skin cells etc which won't ultimately safely biodegrade. That is provided a soak-away won't contaminate food growing land (e.g. salads or herbs). Easy enough to set up a waste pipe with a diversion through a Switched T joint (or you just turn a 90 degree bend around) at the beginning and end of each season. Basic plumbing. For a seaway I'd recommend going down at least a metre cubed and back fill from large rubble at the bottom graded up to coarse sand on top with the outlet buried at 300mm down. Good place to plant next to it something water loving (e.g. willow (as long as it's not too near the house foundations as willow roots cut sideways and are destructive of buildings.) Black Alaskan poplars would be fine in your part of the world. Could be reeds, irises or rushes.

So you see why how much land you have is an issue. The soak-away will build bacterial populations which will digest anything biological and will be more effective the less you use nasty chemicals (bleach strong detergents etc) but will in fact digest up to the level of benzene over time.

The downside of all this is Canadian winters. Will this actually work or will waste water freeze in the pipes? Might dictate depth of pipes etc and then again this isn't 'using' the water very much. Topography matters as it dictates how much slope you have for natural drainage.

Being a little more complex would involve a tank or tanks below ground with a series of baffles which remove sediment etc...this is a classic way of getting 'cleaner' water into a reed bed and would leave less scummy effluent.

Another route (notice how these keep getting more expensive) is to store the water in a tank until spring. As most gray water is warm it is an effective heat store so in the gold-plated world of  'we recycle and harvest everything' the tank is insulated and underlies a conservatory which is heated by the slowly cooling water giving a boost to those early seedlings coming on under glass.

After that you're down to bottling and selling it as a wonder cure, but I don't know how gullible folks are in your neighborhood.

Q: How can grey water be used again for showers, sinks and laundry? Is there a way of purifying the water without it extending the cost?

A: Indeed there is.  The usual way would be to direct the waste water into a biological cleansing system, commonly called 'reed beds'.  This implies a settlement tank followed by primary, secondary and tertiary beds with graded aggregates planted with reeds and other water plants.  There needs to be a fall between each level. Their root associations (which can  function anaerobicly) break down pathogens and the resultant outflow should be cleaner than tap water.  Some recommend aeration as a necessary factor in rejuvenating the water, through fountains or waterfalls. You will then need an energy source (photo voltaics work fine) to pump the water back up to header tank levels. Try a web search on reed beds for detail.

Q: Is the concrete base under a grow bed using gray water necessary?

A: Any impervious material with a suitable outside drain will do.


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