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Building a biological DIY greywater system (with no reedbeds)

October 16, 2012 | Water Harvesting + Reuse | 40 comments | Author:

Our criteria for building the greywater system for the tinyhouse was pretty simple: cheap, made from readily available materials, and effective. We also wanted to use the outputs to irrigate a grove of important fruit trees, as water is very precious here, especially in a dry year.

After many, many hours of research on systems involving reed beds, infiltration trenches, fancy UV zappers and all the rest, we decided, on the advice of permaculture and greywater specialist Ross Mars, to keep it simple, and let the biology do the work.

To summarise the approach (and Ross Mars’ general take of domestic greywater), we decided that the intermittent trickle of water coming from our bath and shower would be best dealt with in a living and dynamic system, rather than in a series of reed beds or trenches.

I should note here that our greywater output is coming from just our bath and shower, so it contains water, a little soap, and the inevitable bits that come off a human when they wash. All the kitchen water is processed via a different system appropriate for blackwater, which i’ll explain some other time.

Reed beds in action – great for some scenarios, but maybe not for ours.
Diagram of a typical domestic grey water reedbed system

We had expected to take the reed-bed route, and pass the greywater through a series of gravel-filled reed beds to clean it up before irrigating the fruit trees with the output. However, Ross mentioned a good point.

Reed beds need to be cleaned out every 5 years or so, as they do clog up with biological material. And of course you don’t want them to overflow with raw greywater into an area not designed to take it, as that would defeat the purpose.

Incase you’ve not have the opportunity to dig out a gravel pit full of reeds and their remarkably extensive root systems, let me summarise the experience – it’s hard and dirty work, and it takes ages. And then you have to wash the gunk off all the gravel, and put it all back again.

Henceforth, the periodic ‘cleaning out the reedbeds’ is usually one of those things on the to-do list that doesn’t get done when it should. Which in turn means many a reed bed greywater system that works great for the first 5 years, and then poorly after that.

What Ross suggested was a very simple system. Super simple, even. And he has just finished conclusive research to show that it does definitely provide as good an outcome as any reedbed system, as far as health and safety goes. But with far less overall energy inputs.

The basic structure of this system is a settling tank, followed by a surge tank, which feeds to a dripline under mulch, to water forest garden plantings.

For our settling tank we used a plastic IBC, and built it a concrete surround. The tank has an inspection hatch at the top , and will need to be cleaned out once a year with a siphon pump to prevent sediment build-up

When this tank is over 3/4 full, it overflows to the surge tank. The water in the surge tank then drains to the dripper system. In this way, the drippers get intermittent watering.

The placement of the inlet and outlet pipes is important in this design. The right angle on the inlet pipe does a lot to dissipate the water’s energy. The way that the raw greywater enters the settling tank pushes the water that has been there longer (and henceforth dropped out most of it’s sediment) further up the tank.

This in turn means that the water overflowing to the surge tank is the water that’s been in the tank for a couple of days already, and therefore is cleaner as it’s particulates have had more time to settle.

The surge tank ensures the water level in the main tank remains fairly constant, which reduces turbulence in the main settling tank, and improves settling.

Once the settling tank is 3/4 full, when a surge comes (ie we empty the bath or have a shower), it overflows to the surge tank through a outlet pipe and onto the driplines around our fruit trees downhill, with the whole system working by gravity.

One of the many beauties of this system is that it doesn’t need any filters as such – there is no filter on the outlet pipe, for example – Ross’s research has shown that designing for fluid dynamics means good sediment settling – which in turn works much better than filters on pipes, and results in a much more overall passive system that is self-regulating. Huzzah.

The fact that the dripline is under mulch is another central point of this system. This way the outgoing greywater is in direct contact with the soil food web (and not with the air, weather and animals) when it gets out into the world.

This in turn means that we’re putting the onus on forest garden soils – a large, stable and distributed ecosystem – to process the greywater in it’s final stage, rather than concentrating the greywater in a pit and relying on the limited (in both space and numbers) biology in there will do the job.

Time to dig a hole for the settling tank, which needed to be below the output of the bathroom

The trough heading down to the future orchard plantings
IBC tank ready to go in
Formwork to keep the poured cement surround in place
Pipes in place – this photo shows the outlet from the settling tank
Inspection/cleaning hatch in place, it’s time to pour the surround
Everyone helped scree the top
And done. pipe outlet to surge tank is on the left, overflow pipe (only relevant in an emergency) is on the right

Our surge tank, a modified olive pickling drum
Completed tanks – inflow from bathroom is the white pipe coming in from the right, outflow to drippers exits out of small black pipe at bottom left
Completed tanks with output pipe to drippers coming out of the surge tank at bottom left – there will soon be a big retaining wall along this cut, sitting on the concrete foundation
Trench for outflow pipe from surge tank, down through the swale and to the future dripper system below
Filled in trench, seen from downside of the swale, ready to be hooked up to a dripline system
The eventual result (sometime soon, once everything grows) – a stable and diverse polyculture that processes the grey water and yields much fruity and herbal goodness

So in short, this system relies on getting the water out into the biological sub-terranean communities of a forest garden as quickly as possible to let biology clean it up and cycle it back through the ecosystem, rather than holding that water and processing in a pit or tank.

In part 2, I’ll explain the octopus and how we’re going about designing the output zone of this system, both in terms of plantings, dripline and all the rest.

Huge and noisy thanks to Ross Mars of for his generosity and good advice in our hour of need. Check out his site for lots of great resources and info about this important factor of sustainable habitats. As Ross says:

Greywater re-use for garden irrigation should be encouraged in both urban and rural  households. It utilises a valuable on-site resource, conserves precious drinking water and reduces the load on wastewater disposal systems.

If applied appropriately to gardens, greywater re-use presents minimal health and environmental pollution risks.

The key to appropriate greywater re-use is user-awareness of the issues surrounding greywater. With increased grey water knowledge, permaculturists can play an important role in promoting the sensible re-use of this household ‘waste’ water.

>> More posts on appropriate technology

>> More posts on permaculture design

>> More posts about water harvesting + reuse

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  • Christopher Milton Dixon October 16, 2012 at 6:38 am | Reply

    In the settling tank are both the top and bottom ends of the outlet pipe open?

    1. gbell12 October 17, 2012 at 7:51 am | Reply

      I second the question! Why are those T-shaped rather than just elbows? Thanks for this, I think you just saved us doing a reed-bed system.

    2. gbell12 October 18, 2012 at 1:47 pm | Reply

      The word from Ross: “Main reason is to trap floating oil, grease, debris so it doesn’t pass into pump or surge tank. The sedimentation tank acts to hold both bottom sludge and oily material, and you only draw water from middle of tank into next one. The T piece also enables a shock load to enter first tank so that it doesn’t pass from one tank to next too quickly. “

      1. Christopher Milton Dixon October 19, 2012 at 1:09 am | Reply

        That still doesn’t answer my question…

        Are both the top and bottom ends of the outlet pipe open? The top looks open in the picture. There’s no mention of that detail in the diagram.

        1. milkwoodkirsten October 19, 2012 at 9:17 am | Reply

          yes! Top and bottom of inlet pipe both open, and same for outlet pipe :)

        2. gbell12 October 20, 2012 at 1:59 pm | Reply

          Yeah, sorry. I sort of hijacked your question. The T-shape (my question) is so that the top and bottom can be open (your question) which allows the muck to float at the top of the inlet (and outlet) instead of being forced down into the settling tank where it would proceed to float back to the top, and ruin the ‘clear’ middle section.

          Kirsten – does this arrangement strike you as almost identical to a septic tank, except for what goes in, and the surge tank?

      2. Milton Dixon October 19, 2012 at 1:27 pm | Reply


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  • Ben Hamley October 16, 2012 at 9:53 am | Reply

    I’ve been using what my Dad would have called a “half-arsed” (i.e. bodgy) version of this system to process laundry water for many years in my urban food-forest. Biology is best! =)

  • Meg McGowan October 16, 2012 at 10:33 am | Reply

    A tip for cleaning your settling tank (you possibly already know this!) is to use a hose for a swimming pool vacuum to create a syphon. We also use this method to clean out the bottom of our water tanks. If you run it into a holding tank of some kind it makes great fertiliser although I suspect that with a grey water system you might need to compost it for a while.

    1. milkwoodkirsten October 16, 2012 at 1:42 pm | Reply

      yep we’ll be siphoning for sure :)

  • Jason Dingley October 16, 2012 at 3:29 pm | Reply

    I have seen a reed bed filter using a small round water tank cut off so it was about half a meter high. The tank was filled with rocks and reeds. Water came in via a pipe on one side, below the rock level, and out the other.

  • Sharon October 16, 2012 at 4:10 pm | Reply

    we are trying to get something similar approved for our house. Council wont allow anything that doesn’t have an EPA approval number, and sadly in Victoria the only approved systems are the high cost, high maintenance, UV zapping, pumped type things. Hoping we can get a biological system that can make use of our water. Very interested to hear what system you have for your kitchen water.

  • Steve Williams October 16, 2012 at 5:23 pm | Reply

    Thanks for this great post. What kind of drip line are you using Kirsten? I’m having trouble finding drip line that will work on my gravity fed rainwater system which has only about 1-2 metres head.

  • John October 17, 2012 at 7:58 am | Reply

    Thanks heaps for this post and detailing why you went with this system, in my ecology courses we learnt that wetlands often move from being fairly open areas of water to dry land over a period of 10 – 200 years (depending on dozens of factors) so when you explained the bit about cleaning the reed beeds out it suddenly clicked. Nice work using the soil food web to do the purification which you would otherwise use the reed beds to do. Very nifty and very permaculture.

    I have a soft spot for reed beds as I like how they look so if I were implementing a similar system I might still put one in after the surge tank so as to minimise sediment build up but I am truly impressed with how simply and practical your design is.

    As always thanks for sharing you experiences.

  • meme1997 October 17, 2012 at 4:24 pm | Reply

    Thanks again for sharing.
    I just wanted to be clear on what you are trying to achieve by having the 2 tanks. If you are storing the greywater it will no doubt get stinky… I am all for a large surge tank. With the subsurface irrigation that you have set up, I don’t see it as a health issue etc. just an ongoing maintenance issue. I look forward to the area coming alive.
    Also I cannot tell by the photos but do you have desludging valves at the bottom of both tanks?
    As always appreciate the work that you are doing.

  • elsumbeaumntarlo October 31, 2012 at 9:53 am | Reply

    Can you write out a parts needed list for this system as Im going to build it. I have the 1000 tank and the olive barrel. What else is needed please and what size and lengths sizes are the pvc pipes. Thanks for all the great info Cheers

  • Eddy Winko October 31, 2012 at 9:21 pm | Reply

    Hi, great article, I’m ploughing through your site with enthusiasm and look forward to implementing many of your ideas in the future.
    You mention that you deal with kitchen water as though it is black water; is that because of legislation in Australia? I had hoped to use ‘environmentally safe’ cleaning products such as Ecover and treat all my water as grey; would this work?
    I also read your article on mulch pit grey water systems; could this not also be used for you grey water from the tinyhouse?
    Looking forward to reading more.

    1. ryan furcini April 16, 2013 at 2:02 pm | Reply

      Kitchen water is considered black due to the presence of organic materials such as food waste. I suspect that legally you cannot treat black water as grey water. But It may be worth a shot, especially if you have screens over your kitchen sinks drains.

      1. milkwoodkirsten April 16, 2013 at 3:34 pm | Reply

        Yep that’s why this system does not process our kitchen water, only our bathroom water

  • Paul December 31, 2012 at 9:37 am | Reply

    This system is completely overkill for something so simple as bathwater. The “septic/settling” and surge tanks are completely unnecessary. Exactly how much biomass/sediment do you plan to wash off yourselves!? LOL The simple way to handle greywater from showers, tubs and laundry is a branched greywater system piped to mulched basins planted to fruit trees, as explained very well by Art Ludwig at in his book ‘Building An Oasis With Greywater’ and can be done at a fraction of the cost that you spent on your “engineered” system.

    1. milkwoodkirsten December 31, 2012 at 10:21 am | Reply

      Hi Paul, if you read back thru our other posts on greywater re-use you’d probably have picked up that we have built previous versions of mulched pig greywater systems similar to the ludwig designs (tho not exactly as it’s really hard to get the branching pipe brackets that he specifies as being an essential part of the system in Aus), but with our soils they just didnt work very well (we just ended up with manky ponds under mulch which didnt drain sufficiently, due to soil type) – nothing works in every context :) – you would be surprised how much sediment *does* infact build up in these types of greaywater systems, so in order to output that water to dripline under mulch (much better for our context than mulch pits) the sediment needs to be removed or the whole dripper system stuffs up. Multiple PHD’s have been written on this type of system in Aus looking at its effectiveness, and so far this system is working far better to create growth where we need it that our mulch pit system… we Love Art Ludwig’s work but he himself says that branched branched greywater mulch pit systems aren’t necessarily appropriate for every context :)

  • Abdullah Eyles February 25, 2013 at 11:07 pm | Reply

    Dear Kirsten,

    Many thanks for this excellent article (in fact your whole website!).

    I was planning to follow your example and make myself a greywater system after having given up due to the reed bed requirements m-a-n-y years ago.

    But today I read a web page which put me off once again; therefore I’d like to hear your opinion on the problems outlined on this page (especially with regard to storage of greywater):

    Have you had trouble with stagnation or is your throughput enough to prevent this?

    Many thanks,

    Abdullah Eyles,
    Ankara, Türkiye

  • David March 30, 2013 at 3:22 am | Reply

    This is really interesting, all the different views and suggestions.

    I have 4 small design / concept Q’s please;
    1. Does the plan include (or not) a lower outlet for cleaning sludge?
    2. How would one remove the sludge without removing the standing water above it?
    3. Wouldn’t the water stink / stagnate as most of it just sits there. (The outlet is 3/4’s of the way up the holding tank. What shock surges come from the bath?)
    4. Since creating this would you change any of the design?

    My folks live near Budgewoi and they are not allowed to pump the water onto their gardens. I think using the grey water is a super, cost saving idea. The Wyong Council does (love to) charge them excess water for keeping a garden as green as needed, when they are allowed to use the hose pipe.

    When living on a 12 acre turf farm in Greenbank, QLD (1991-1994) our greywater just went outside via a pipe and straight under heavy mulch and onto our Banana trees. The water was from our washing machine and shower. The kitchen sink water went into the septic I believe.

    The water exited the poly pipe via large nipples placed along the PP every 12″ to 18″ (30 to 45cms)… The end was bent over and tied. It’s simple and it worked. There was almost no smell, except a tiny teeny bit in summer. Only noticed when you lifted the mulch to check on the nipples once a week. Nipples were replaced or cleaned as needed. The Bananas were yummo and plentiful. Being in the UK for almost 17 years… Not meaning to sound daft but… Why do we need to use these systems? I’m not being argumentative either. Has something changed since we left? :))

  • Gelu Botezan April 4, 2013 at 3:10 am | Reply


    I can’t get it from the text! Is this a no frost area your are living in?
    I actually live in continental Europe(western Romania) with temps like -20 C in the winter.
    I suppose you do not have this climate there sin’t it?

    1. milkwoodkirsten April 4, 2013 at 6:09 am | Reply

      Yep we get frosts and get nights of -10c ish?

      1. Gelu Botezan April 4, 2013 at 8:20 pm | Reply

        thanks for your answer, I meant we really have cold winters with day temps of -20 and lower, and this for weeks sometimes. Nights is of course even colder I
        I just wonder if a similar sistem would wor for me as the vegetation is actually dormant for 3 to 4 months. I can’t think of storing the water in a tank for the winter.

  • David T April 5, 2013 at 10:08 pm | Reply

    Where did you get your IBC from please? Do you remember what it roughly cost?

    Was it one that was certified chemical free and leak free?

    I asked above; “why we need these systems”… not to be argumentative, but to understand why we shouldn’t just run it straight under the mulch. Under the mulch to ensure it doesn’t touch leaves etc and also so the precious water goes straight to where it’s needed, the soil/root systems. Sorry if the way I asked was considered rude or offensive. It was not meant to be that way.


    1. milkwoodkirsten April 6, 2013 at 6:43 am | Reply

      Hey David, this tote was 2nd hand and previously had diswashing liquid In it… Was about $100 I think…

      The point of the system is that if you run straight to drippers, there will still be gunk in the water which will clog yr drippers. The whole point of this system is to settle out the gunk so the water entering the dripper system comes out clean enough to ensure the system works long term… The idea being that all the water entering the system reaches the drippers in a day or so.

      For our climate, soil types and drought patterns, we reckon this is a good system for keeping a small orchard of valuable fruit trees thriving long term, while utilising a waste resource

  • frugalque May 15, 2013 at 6:14 am | Reply

    Great system. We have a greywater system (or two). One from our washing machine and one from our kitchen. it works great. Very simple design with pvc pipes. We will also be installing another system soon from one of our bathrooms. That is on the back of the house but it will be simple also. One day, i will do a write up and take pictures … :) I encourage people to just do it. It really isn’t rocket science and I love not wasting all that water.

  • [email protected] June 9, 2013 at 2:57 am | Reply

    Hi there. The information is absolutely awsome. Question. Is it possible to have an open tank instead of a closed lid? are there issues with smells?

    1. milkwoodkirsten June 9, 2013 at 9:02 pm | Reply

      The lid is recommended so that nothing (or no-one) falls in, partly because that would suck as an experience and partly because you dont want the inlets or outlets clogged with dead lizards, or anything else.

      Plus you want your greywater getting back into a stable biological system (ie the soil) as soon as possible without coming into contact with too many things like flies, insects, etc.

      The holding tank doesn’t smell bad, but the whole point of it is to let the solids drop out of the water before the water progresses to the drippers, so i assume at the point before it was due to be cleaned out (once a year) there’d be a buildup of gunk on the bottom that wouldn’t smell great.

      1. Sixdor June 24, 2014 at 12:15 pm | Reply

        Could you have used the drain tap (approx.) 50mm on most IBC to drain the sludge straight out for collection or into a/your blackwater system e.g. biomass digester .

  • Vic October 29, 2013 at 4:52 am | Reply

    Hi Kirsten. I’ve been wanting to install something like this on my site here in Argentina since I first read this post last year. I’m getting closer to being able to, but wanted to ask how much of a drop you need between the inflow of grey water and the tank? Mine is direct from kitchen sink and washing machine, but my land is totally flat, grrr. Also, you mentioned that you have another system that might be better suited to black water treatment… Are you planning to post on that? (Would love to see it!). Thanks for always being such a huge source of inspiration!

  • gardenange May 24, 2014 at 12:11 pm | Reply

    HI Kirsten-

    We have an old-fashioned septic system on 1.25 acres. I’m now thinking to use the gravitational energy of the pumped effluent through a similar system to yours. Problem is, ours is septic effluent, not grey water. I can’t find much about septic effluent treatment, other than traditional drain field systems. We have a downhill orchard with dripper line already installed, and it seems like a match made in heaven. OK so its black water, but there are two mitigating factors: we plan to start using a dry composting toilet, which will remove some, but not all faecal matter (I confidently predict our teen daughters won’t convert to using the composting system!), secondly, its already gone through a septic tank. My question is, are these really mitigating factors (with respect to pathogens), or am I kidding myself? The other issue is sodium in the water. We use the best cleaners we can easily get, but we still have dishwasher and washing machine. Thoughts? Finally, are you running out through pressure-compensated dripper line? What head are you supplying, and are you confident that you have removed enough particles to obviate an additional filter?

  • Angus Matin October 3, 2014 at 6:40 am | Reply

    This is good for someone who has the space and money and inclination to use cement, buy plastic tanks, etc… Some of us are looking for even simpler, less expensive, solutions that use as many living biological factors as possible, and as little industrial inputs as possible. To make my small (20′ by 5’?) pond I mixed in sodium bentonite about 5 or 6 inches into the native soil/clay. It’s only partially full of water and I already planted water cress, native reeds, duck weed, etc, in anticipation of the winter rains. I am presently digging out a short (5 feet?) run of impermeable nature (maybe I’ll use more bentonite, maybe I’ll use cement, or even an old tub) which will be filled with gravel/rock, then mulch, then mushroom logs inoculated with oyster mushrooms, all of which will be relatively easy to remove and replace when/if necessary. After the fungal filter the water descends into another impermeable bowl where reeds grow naturally (i.e. right in the mud) then down some flow forms where watercress and other plants will anchor themselves and into the pond. The water that will fill this pond will be a mix of washing machine greywater, roof runoff and rain. Overspill from the pond will go directly in the garden just below, or will be siphoned down the hill to the lower garden when needed.

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  • Jeff October 30, 2014 at 8:15 am | Reply

    I’m curious how you joined/sealed your PVC to your pickle barrel. I have almost exactly the same barrel that I’ll be using as my gray water settling tank. My surge will be handled by “Infiltrators,” (brand name you might not have down there). These offer a combination of leach and surge at the same time.

    I will place the tank on gravel but I want to get a reasonable (perfect is reasonable ;) ) seal on my inlet and outflow.

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