Greywater is a fabulous, though often underused, household resource that should be used wherever possible. Here’s a home made 3 bathtub greywater system that’s simple but effective.
If you live in an area where water is precious at certain times of year (and when is it not?) then catching, storing and using every drop you can to create a more liveable home and surrounds is an excellent idea.
At Melliodora in Victoria, the studio cottage does its best to do just that, by catching, filtering and re-assigning the greywater to useful purposes in the garden.
While this design will not suit everyone, it will suit some, and it’s a simple, cheap and effective way to deal with, process and make the most of a small household’s greywater.
Grey vs Dark Grey vs Black Water
There’s a couple of types of water that come out of a regular Australian household, which are commonly broken down into a few categories. Opinions on what goes where sometimes differs, but generally speaking:
Greywater – water from the shower/bath, handwashing sinks, washing machine – water that has a low loading of bits in it other than water, and minimal human pathogens (ie poo).
Dark Greywater – water from the kitchen sink and/or dishwasher – water that has a higher loading of proteins, fats etc than greywater, and more ‘bits’.
Blackwater – water from the toilet or elsewhere in the house that has a high level of potential human pathogens (ie poo). This type of waste water is *not* suitable for the below greywater system. If possible, build a lovable loo or wheelie bin compost toilet instead (or a commercial composting toilet system), and use your precious water for things other than flushing, which wastes not one but two valuable resources in the process.
The system below is a greywater system that also deals with a small amount of dark greywater – as it processes the outputs of a shower, a kitchen sink, and a washing machine.
Greywater System Pointers
With any DIY greywater system, there’s a few basic things that you want to achieve with your water:
First in, last out – you want to filter the water as much as possible, and ensure no water can ‘jump the queue’ somehow and come out the other end unfiltered. This means planning an appropriately sized system for your needs, and making sure the water goes where you want it to.
Maximize dwell time – the more filtering that your water gets in the system, the better. Because this means more time for the microorganisms int he system to do their thing, and clean up your water as much as possible.
That said, every day brings more water, so you also a system that easily manages the outflow, and a plan for where to point/use the water next, after it’s been through the system.
Minimize inputs – to the system, in the sense of things like soap, goop, shampoo etc, which make the water more alkaline. Everything you use, or do, has an effect somewhere else in the system. The same is true on a town-greywater level, but we don’t notice the effects.
In a home-scale closed loop system however, you do. So use minimal amounts of greywater friendly products to ensure your water is as clean as possible.
Biology works – all hail biology. The more biology you can get onboard to help you with filtering your water, the better. Getting biology do the work minimises complicated systems, external inputs, and is a DIY regenerative approach that can be re-started if an aspect of the system breaks, without buying another one off the shelf.
The below system uses worms, reeds, microorganisms and a cropping bed.
*a note that with the exception of the scoria rock, this system was completely sourced from junk – scavenged parts from the tip, and friend’s backyards. So the total cost of building this system was about $50.
3 Bathtub Greywater System:
This system was designed by David Holmgren and built with friends. It’s context-driven, so not suitable for everywhere in the world, but it’s a great solution to the needs of this sized building, in this climate, on this budget.
We took the below photos while we were giving this greywater system a clean-out. It’s about 5 years old at this point.
Worms, Reeds, Sit, Onward…
So the inputs of this greywater system are from the studio’s shower, kitchen sink, and washing machine combined.
The input water goes in the top tub which is a wormfarm, drains to the second tub which is a reed bed, and then sits in the bottom tub until further inputs cause an overflow, at which point the filtered water flows slowly down a ditch drain to a main crop growing bed.
Tub one – Worms
The first tub of the system is a wormfarm. The worms appreciate the regular moisture, and eat up any solids that arrive out of the inlet pipe from the kitchen sink.
The inlet pipe is open at each end, and has a series of small holes all the way down it’s length to allow for even-ish distribution of water into the tub.
It’s important to keep this first tub well drained so the worms don’t drown, so in this tub the water goes in the top, then drains straight through to the bottom outlet.
The base of the worm section is raised on plastic arms holding up a wire mesh (called ‘bar chairs’, they’re used in concreting to hold up the re-bar – you could also use bricks). On top of this sits some old shadecloth which acts as a sieve – worms and their solids stay in the tub, liquids (mainly the greywater) drain out to tub 2.
The shadecloth also makes this tub easier to empty every two years or so, like this day. After harvesting most of the worm castings, fresh straw is put down, followed by a small layer of castings (and worms!) and then covered with more straw.
The system is now set for another 2 years of processing the household waste and water, while building up another valuable harvest of worm castings in the process.
Tub two – Reeds
The second tub contains scoria – a local rock that’s close to pumice, with lots of cavities for microorganisms, and Umbrella Sedge Cyperus eragrostis – which is a hardy wetland plant suitable for this climate.
The idea for this tub is that the water comes in at one end, and is pushed under tile baffles in the middle of the tub to make a longer journey for the water before it can reach the outlet at the other end of the tub.
While the water is in this tub, it’s filtered by the rocks and their resident microbiology, and the roots of the reeds also.
The reedbed part of this kind of system is often the trickiest to renovate and clean, as the roots of the reeds get tangled in the rocks and are generally bloody hard work to dig out, clean, and re-install. In this comparatively small-scale design, this task is manageable because of the tub’s size.
Tub three – Holding Pond
The water comes out of tub two and into the holding pond.
Once this fills up, it overflows gently to a clay half pipe and then onto a shallow earth drain which deposits the trickle of outgoing water into a large garden bed used for summer main crops like corn, wheat etc. Green manures are grown in this bed over winter.
The outputs of this third tub could alternately go to a forest garden, shade trees or similar, depending on the needs of the home.
The harvests of this system could be said to be: fertilizer in the form of worm castings plus a main crop of veggies each summer. And a closed loop greywater system that harms no waterways, and empowers it’s residents to be more self-reliant. Wins all round.
As with any system, there’s always room for improvement, and these will surely come over the years. But for now, it’s a great little system that works well to process a small household’s greywater outputs – with minimal maintenance and cost, plus some beneficial outputs.
Thanks to David Holmgren for his help (and building the system in the first place!).
- Building a biological greywater system at Milkwood Farm
- Water harvesting + reuse – articles on Milkwood.net
- Greywater Action – lots of great resources here
- Oasis Design – amazing greywater section
- Harvesting Rainwater’s greywater section