Backyard greywater - the why and wherefore.

Lars Fields, author of a fantastic guide to building a greywater wetland in your backyard (available in the Frog Watch feature section) discusses what drew him into world of phytoremediation and details some of his adventures and early experiences. It is a personal companion piece to the factual information contained in the previously published guide.

I basically have no idea what I'm doing. I'm sort of making it all up as I go along. Where did this all begin? How did I become interested in greywater, of all things? And bogs? I'm pretty sure my neighbours are beginning to talk about me. Why would anybody want to process their own wastewater? And be enthusiastic about it? That's a good question...

+ 66 kb The bog portion of Lars's phytoremediation wetland. While Lars heartily recommends native plants, you may find some introduced species in this photograph.

We're all becoming increasingly aware of the huge numbers of ecological roadkills that line the freeways of commerce and "progress". This planet is currently hosting it's 6th Mass Extinction in the 2 billion years that life has existed on it (ranking up there with the asteroid that wiped out the dinosaurs). Worldwide, thousands of species are lost every year - about 80 a day, and increasing. Most extinctions are due to loss of habitat, as humans modify or destroy entire ecosystems. Pollution, exotic species introduction and disease transfer doesn't help matters. We'd like to blame corporate bigwigs and politicians for these disasters, but at the end of the day, it's our collective actions as consumers that are causing the far greatest amount of habitat destruction and foreign species introductions, not oil and mining companies. The problem isn't only out there in the rainforest, it's in our backyards as well.

We all have deep complicity in this habitat destruction. I personally don't know of a single individual (including myself) who is leading a sustainable life. To varying degrees, we're all overspending on our environmental credit cards, living well beyond our ecological means, creating deep debt measured in massive reductions in biodiversity. Modern agriculture and car-dependent suburban sprawls are probably the main reasons why 95% of our wetlands have been drained since european invasion - it's quite likely your house was built on a drained wetland. And while corporate bigwigs might indeed be conspiring to take over the world, our purchasing decisions at the plant nursery down the street are actually causing much more harm to Australian ecosystems, because most gardeners are likely to be buying white birch trees and frangipanis than native grasses or banksias. Even being a vegetarian in Australia doesn't win you many eco-points. For every kg. of bread we eat, 7 kg. of australian topsoil is lost and every time we buy Australian-grown rice, we're probably drawing more salty water into the soils along the Murray.

These are quite depressing realizations. If every individual - even the most rabid environmentalists I know - aren't living sustainably, then how will our society as a whole ever become sustainable? Is the seduction of convenience so irresistible that we are powerless to slow down, let alone halt, the accelerating loss in biodiversity? To get a rough idea of your personal environmental impact, try an online "ecological footprint calculator" - there are many available. Because of these realizations, our family was determined to start learning how to be sustainable, and reducing our consumption of water was one of the first things on our list.

The typical Melbourne household consumes more than 700 litres of water every day (source: Yarra Valley Water). That's 260,000 litres per year!. 1/4 to 1/3 of that drinking quality water is used for flushing the toilet and goes to the sewers as "blackwater". Another 1/3 is typically used to water the lawn and garden. The rest is used for showers, baths, laundry, dishwashing, etc. The wastewater that results from those activities is known as "greywater", which typically contains relatively small concentrations of soaps and detergents, along with a bit of organic waste like food, hair, and dirt. Even though, unlike blackwater, greywater is a minimal health threat, the two wastewaters typically end up mixed together, going down the same drains to the same sewage treatment plant, and from there usually to the ocean. Every time I flush the toilet or do the laundry, I'm doing harm to a downstream ecosystem. And every time I put the hose in my backyard pond to top it up, I'm likely to be diverting water from some wetland ecosystem upstream. Those are some of the negative impacts of our modern water and sewage systems.

Though it would be largely a symbolic gesture at first, I decided to become more involved in my own wastestreams - to divest myself as much as possible from the public wastewater system. I decided to start cleaning up after myself, rather than just sending it "away" for someone else to deal with. So first thing, I needed to learn how to deal with my own wastewater. I wanted a cheap, simple, elegant, and flexible solution. One that didn't simply defer the problem until later into the future, so standard septic tank systems were out, even if I could consider installing one in my rented urban house.

Our family had already acquired a worm composting bin to handle most of our solid organic waste, which greatly reduced the volume in our trash bin, while giving us great organic compost and liquid fertilizer. So I had already gained a lot of faith in biological systems for dealing with waste. For many years, I had also been following the work of various organizations and individuals around the world who were using a wide range of constructed wetland systems to clean and process a variety of wastewater streams, from industrial to municipal. So my thoughts were that I could take a problem waste product, and turn it into an backyard environmental resource, by using the nutrients in greywater to fertilize a wetland planted with indigenous plants, providing a tiny oasis for indigenous wildlife, and removing most of the nutrients in greywater and thus make it more usable in the yard. But I couldn't find any DIY "instruction manual" that spelled out in detail how to go about constructing a household-scaled indigenous-planted greywater wetland for a backyard. How big does it need to be? How deep? Which plants should I use? What should I use as a substrate? Which waste streams can I use? What's the best way to "harvest" the wastewater and get it to the bog? What are the health and safety issues?

+ 37 kb Species of Ranunculus and Triglochin (immersed form) on the surface of the water in Lars's wetland.

After researching enough related material to convince myself that I wasn't going to create a health hazard, I decided to just go ahead and build a "test" bog. A small one that would handle just a portion of our greywater, if only to see how it worked out. My reasoning was that if I was eventually going to build a full-scale one, I first needed to get a feel for how much greywater my family produced. I really had no physical idea as to how much water hundreds of litres per day really was. It sounded like a lot, but it really was just a number to me - did it represent a puddle or a pond? As the kitchen sink was the easiest drain to access, I could at least find out how much was produced from this one source, and then extrapolate from there. So I unscrewed the drain pipe from my kitchen sink and put a bucket underneath (I have since found out that dishwasher and kitchen sink water is generally not good to use in the garden - it's sometimes called "brownwater" to delineate it from other greywater sources. To be on the safe side, stick with laundry, bath and shower water). I dug a small pit (about 2 sq. meters by 1/3 meter deep), lined it with some black polyethylene builder's plastic I had scavenged (with cardboard and old carpet underneath to protect the plastic), filled it with gravel, and stuck in various wetland plants that are indigenous to Melbourne. When the bucket under the sink filled up, I would simply dump it into one end of the bog.

I half expected that the nutrient levels would be too high and that most of the plants would die. I also expected the bog to produce bad odours. But nearly all the plants thrived and it never smelled bad (though if I let the greywater sit in the bucket for more than a day or so, it did start to smell - it's best not to let greywater sit around for more than a day). I also expected to see more mosquitoes around, but that didn't happen either. As long as there is no standing water, they have no place to breed. Technically, what I built was called a "sub-surface flow wetland", where a gravel substrate was continuously waterlogged, but it was designed so that water never flowed over the surface, so there weren't any open pools or puddles. Although I called it a bog, the gravel substrate was completely firm enough to walk on. With a layer of mulch on top of the gravel, it looked like a typical garden bed filled with healthy native plants.

One unexpected thing that did happen was that our total household water use went down. If you look on your water bill, it will tell you how much water your household consumes and how much sewage your house produces (usually in megalitres per quarter). Of course, I expected that the amount of sewage we produced would decrease by a fraction, as we were now diverting a portion of that wastewater into the bog. But what also happened was that since my family was now more conscious of our water use, we tended to use less water - a lot less. Simply thinking about water caused us to change our habits, like not letting the faucet run while washing the potatoes or brushing our teeth, being more efficient when washing the dishes, taking shorter showers, and waiting for a larger load before doing the laundry. All of these changes in habits added up to big reduction in our water use in a very short space of time. And it wasn't difficult, it wasn't like we had to continually think about our water consumption - the old habits simply got replaced by new ones without us really noticing. It also changed what sorts of things we would consider putting down the drain, which in turn affected which cleaning products we chose to buy - if I didn't want those products going into my bog, I began to think that maybe they shouldn't be going into any aquatic system.

+ 64 kb A section of Lars's bog showing species of Alisma, Persicaria, Crassula, Schoenoplectus, and Triglochin (in emergent form).

As our baby became a toddler, we moved to a new rented house with a larger yard. We dismantled the old bog and used the plants to start a larger bog in our new yard. Based on what I learned from that first experience, and our new water consumption habits, I decided to try and build the new bog to handle all of the greywater from our house. Our family of three (one of them a toddler who wears cloth nappies) has now consistently reduced our water consumption to less than 200 litres per day, of which more than half of that ends up as greywater which is suitable for adding to our bog. I roughly estimated that, once established, a bog around 5 square meters and about 40 cm deep might be enough to handle most, if not all, of that greywater. The water enters the bog in one corner and after travelling through the wetland gravel substrate and plant roots under the surface, it drains into a pond, from which we bucket any excess "cleaned" water for use around the garden. In the summer the wetland plants really soaked up a lot of water, due to increased evapotranspiration, but now that cooler weather has come, the pond will overflow if we add all of our household greywater without removing sum from the outlet end. So I'm now planning on installing a float-switch water pump that will automatically pump the excess pond water to garden beds or a water storage tank. Processing greywater through a wetland is, in a sense, a bit of overkill, as you can water most garden plants with greywater directly. But it certainly doesn't hurt to have a least some of those phosphates and other salts removed before watering my natives, as many australian plants don't like too much fertilization. Greywater also goes stagnant if you try to store it for more than a day or so, but once going through the bog and having most of it's nutrients removed, the water is clean enough store for extended periods of time. Plus, during these times of water restrictions, I feel better about having a pond that doesn't need topping up with city water from the hose. And according to our water bill, the wastewater from our house going to the sewage treatment plant (and on into Port Phillip Bay) is now less than 100 litres per day, and shrinking.

The wetland has been planted for about 5 months now, and the plants are thriving. The great thing about wetland plants is that they're really easy to grow, and many of them grow very fast. Within 2 months the bog was essentially an established wetland garden, with a wall of cumbungi over 2 meters tall and growing, and large sprays of alisma flowers. The plants certainly appear as healthy as any I've ever seen. I've recently stocked the pond area with several more indigenous wetland plants like milfoil and nardoo, and they seem to be doing great. Even a gardener with the blackest of thumbs can grow a wetland garden, as it seems impossible to overfertilize them, at least with greywater. And since they like wet roots all the time, you can't really overwater them either. It's also very easy to add a greywater bog to an existing pond.

+ 36 kb A mantis surveys the greywater pond from amongst the water plantain (<i>Alisma plantago-aquatica</i>).

And despite my urban surroundings, the wildlife in my formerly ecologically barren urban yard has already increased slightly. I've noticed a kind of mantis that I never saw before. Potter's wasps land on the water surface to soak up water for their constructions on our outside walls. And dragonflies have started buzzing around. Even the mole crickets seem to have convened around the bog. My son certainly loves it. And although we live more than a kilometre from the nearest frog habitat, I'm keeping my fingers crossed that they'll eventually find our little oasis, hopefully by "leapfrogging" from other neighbour's ponds. I've done some rudimentary water testing, and although it is a bit hard (around 220 ppm), it's certainly within the range for most Victorian fish species, so I'm ready to introduce some southern pygmy perch (Nannoperca australis), a small species of fish that used to be common in the Melbourne area.

From these experiences, and from some material I later found (especially the work of Leigh Davison) I put together a basic description of how greywater wetlands work, as well as some guidelines for building your own backyard greywater bog.

This isn't really well-trodden territory, and the effectiveness of a greywater bog will vary depending on differences in amount of seasons, sunlight, microclimate, altitude, greywater sources, cleaning products, plants, the age of the wetland, etc. For these reasons, it's very difficult to be definitive about these guidelines. It's nearly impossible to be predictive about such a complex system as a wetland, especially one that exists outside of laboratory conditions and is influenced by such a complex set of variables. I've tried to cover most of the design issues and point out potential solutions to the mistakes that I made along the way, but I'm certainly no expert and it's likely I've overlooked things or not found the most elegant solutions. In other words, what I've written is certainly not the first or last words on the subject. There's lots of other general information on the internet about related subjects like "phytoremediation", "reed beds", "constructed wetlands", and "subsurface flow wetlands" that might provide inspiration and other solutions.

In any case, I hope it's helpful for you to use these general guidelines to build your own greywater wetland, in your own way, making your own discoveries and errors, and then sharing your experiences with other greywater bog builders like myself. Thereby, collectively we can zero in on a range of effective solutions. Feel free to email me if you have any suggestions or questions.

Author: Lars Fields, April 2004

Further reading

Lars's greywater wetland design guidelines are available as a feature article within the Frog Watch project.

• Frog Watch feature articles